Abbreviations
Imperial
|
Metric
|
|
|
AC
|
acres
|
m
|
meter
|
SF
|
square foot
|
km
|
kilometer
|
lb
|
pound
|
ha
|
hectare
|
oz
|
ounce
|
g
|
grams
|
mi
|
mile
|
kg
|
kilogram
|
ft
|
foot
|
gpt
|
grams per tonne
|
|
|
|
|
Conversions
Imperial to Metric
|
|
Metric to Imperial
|
Imperial Measure
|
Metric Unit
|
|
Metric Measure
|
Imperial Unit
|
2.47 acres
|
1 hectare
|
0.4047 hectare
|
1 acre
|
3.28 feet
|
1 metre
|
0.3048 metre
|
1 foot
|
0.62 mile
|
1 kilometre
|
1.609 kilometres
|
1 mile
|
0.03215 troy ounce
|
1 gram
|
31.1035 grams
|
1 troy ounce
|
0.02917 troy ounce per ton
|
1 gpt
|
34.2857 gpt
|
1 troy ounce per ton
|
1.102 short ton
|
1 tonne
|
0.907 tonne
|
1 short ton
|
2.2046 pounds
|
1 kilogram
|
0.4536 kilogram
|
1 pound
|
I-M Mine Property, California
Our principal mineral property is the I-M Mine Property.
I-M Mine Project Location, Description and Access
Property Location
The I-M Mine Property comprises approximately 175 acres (71 hectares) surface land and approximately 2,800 acres (1,133 hectares) of mineral rights located near Grass Valley of Nevada County in northern California, USA. The I-M Mine Property is situated in the Grass Valley-Nevada City Mining District along the western slope of the Sierra Nevada, as shown on the overview map and regional map in Figure 1 and Figure 2, respectively and is located approximately 60 miles northeast of Sacramento, CA and 90 miles west of Reno, NV.
Figure 1: Idaho-Maryland Mine Property Location Overview
Figure 2: Idaho-Maryland Mine Property, Regional Map
Property Description
The recorded owner of the surface land and mineral rights associated with the I-M Mine Property is Rise Grass Valley Inc., a Nevada Corporation and subsidiary of Rise Gold Corp. Rise Grass Valley Inc. purchased the I-M Mine Property, inclusive of its mineral rights from the Grantors of the BET Group Estate, as described in the Quitclaim Deed (Document #: 20170001985), on the 25th of January 2017 and additional surface land described as the Mill Site in 2018.
Surface Rights
The I-M Mine Property surface rights include three parts of fee simple land, (1) Idaho land representing 56 acres (23 hectares), (2) Brunswick land representing 37 acres (15 hectares), and (3) the Mill Site property representing 82 acres (33 hectares) as displayed in Figure 3.
The I-M Mine Property consists of parcels of surface land located in portions of Section 26 and 36, Township 16 North - Range 8 East Mount Diablo Base and Meridian (MDM) and Section 31, Township 16 North - Range 9 East MDM as detailed in Table 1 and displayed in Figure 3.
Table 1: Idaho-Maryland Mine Property - Surface Land Legal Description
Parcel
Number
|
Description
|
Lot Size
|
09-550-32
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN N 1/2 26-16-8
|
20,908 SF
(0.48 AC)
|
09-550-37
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN NE 1/4 26-16-8
|
4.47 AC
|
09-550-38
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN NE 1/4 26-16-8
|
40.1 AC
|
09-550-39
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN NE 1/4 26-16-8
|
42,668 SF
|
344 CENTENNIAL DRIVE GRASS VALLEY, CA 95945
|
(0.98 AC)
|
09-550-40
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN NE 1/4 26-16-8
|
5,662 SF
(0.13 AC)
|
09-560-36
|
SEC 26, TWN 16N, RNG 8E, MDM, PTN N 1/2 SE 1/4 26-16-8
|
10.25 AC
|
09-630-37
|
SEC 36, TWN 16N, RNG 8E, MDM, LOT 6 BET ACRES
|
21.8 AC
|
09-630-39
|
SEC 36, TWN 16N, RNG 8E, MDM & SEC 31, TWN 16N, RNG 9E, MDM,
LOT 7 BET ACRES
|
15.07 AC
|
06-441-03
|
SEC 36, TWN 16N, RNG 8E, MDM & SEC 31, TWN 16N, RNG 9E
|
15.19 AC
|
06-441-04
|
SEC 36, TWN 16N, RNG 8E, MDM & SEC 31, TWN 16N, RNG 9E
|
0.85 AC
|
Parcel
Number
|
Description
|
Lot Size
|
06-441-05
|
SEC 36, TWN 16N, RNG 8E, MDM & SEC 31, TWN 16N, RNG 9E
|
50.01 AC
|
06-441-34
|
SEC 36, TWN 16N, RNG 8E, MDM & SEC 31, TWN 16N, RNG 9E
|
16.01 AC
|
Figure 3: Idaho-Maryland Mine Property, Surface and Mineral Land Holdings
Surface Land Obligations
Fee simple ownership entitles the owner to all rights of a property, which are only restricted by law or private restrictions, such as zone ordinances or covenants. Fee simple owners retain possession of their property permanently, assuming all obligations to the land are met.
The surface land is subject to a tax lien imposed by and payable to Nevada County. The parcels comprising the surface land are currently assessed by Nevada County at a total of US$4,141,617 and have a combined annual property tax of US$45,242 for the 2021 tax year. The total amount includes County taxes and Agency taxes. The I-M Mine Property remains in good standing with property taxes for the 2020 tax year paid in full. Property taxes for the 2021 tax year of $22,621 is due on Nov 1st, 2021, and $22,621 is due on February 1st 2022.
The Nevada Irrigation District supplies treated water to the I-M Mine Property. Water to the Brunswick land is delivered from the Loma Rica System, while water to the Idaho land is delivered from the E. George System. A nominal service fee is charged.
The secured loan from Eridanus Capital LLC is registered against the property by a Deed of Trust filed with the Nevada County Recorder. There are no further interests registered against the title of the surface rights.
Land Designation
The Brunswick land and Mill Site is located approximately 1 to 2 miles southeast of the city limits of the City of Grass Valley in Nevada County. The Idaho land is located on Idaho-Maryland Rd adjacent to the city limits of the City of Grass Valley in Nevada County. The I-M Mine Property in relation to city limits is shown on Figure 3. Due to its proximity, the I-M Mine Property is located within the City of Grass Valley's planning area boundary, with Brunswick and Mill Site land located in the "Long-term Annexation" and Idaho land located in the "Near-term Annexation" Sphere of Influence. Based on the City of Grass Valley 2020 General Plan, the planned land use designation for the Brunswick land remains "M-1" Manufacturing/Industrial, while the planned land use designation for the Idaho land is "BP" Business Park (CoGV-CDD, 2009).
Each of the parcels of Brunswick land and Idaho land are positioned within the County's "M1" Light Industrial Zone. Within the "M1" District, surface access to subsurface mining (e.g., vent and escape shafts) is allowed with a Use Permit (Nevada County Code § L-II 3.21.). Mineral exploration, however, is distinct from the definitions of "subsurface mining" and "surface mining." Exploration involves the search for economic minerals through the use of geological surveys, geophysical or geochemical prospecting, bore holes and trial pits, and surface or underground headings, drifts, or tunnels (NCC § L-II 3.22(B)(5).). Exploration diamond drilling on M1-Industrial Land is an allowed use and does not require a discretionary permit provided that no water is discharged offsite and disturbance per site is less than 1 acre and 1,000 yd3 material (NCC, 2017).
The Project area is private land and no permits or consultations with the US Bureau of Land Management (BLM) or the US Forest Service (USFS) are required.
Mineral Rights
The I-M Mine Property consists of mineral rights on 10 parcels, including 55 sub parcels, totaling 2,800 acres (1,133 hectares), of full or partial interest, as detailed in Table 2 and displayed in Figure 4. The mineral rights encompass the past producing I-M Mine Property which includes the Idaho and Brunswick underground gold mines.
The original mineral rights were granted at various times since 1851. Through various patents and agreements since the original grants, there has been a succession of ownership of the mineral rights.
The Quitclaim Deed describes the mineral rights as follows:
The I-M Mine Property consists of all rights to minerals within, on, and under the land shown upon the Subdivision Map of BET ACRES, No. 85-7, filed in the Office of the County Records, Nevada County, California, on February 24, 1987, in Book 7 of Subdivisions, at Page 75 et seq.
The I-M Mine Property consists of all rights to minerals within, on, and under the land located in portions of Sections 23, 24, 25, 26, 35, and 36 in Township 16 North - Range 8 East MDM, Sections 19, 29, 30, and 31 in Township 16 North - Range 9 East MDM, and Section 6 in Township 15 North - Range 9 East MDM and all other mineral rights associated with the Idaho-Maryland Mine.
The mineral rights are defined as parcels and sub parcels in a Quitclaim Deed (Document #: 20170001985). All property is described in that Quitclaim Deed by Idaho Maryland Industries Inc. in favor of William Ghidotti and Marian Ghidotti, his wife as tenants in common, dated June 10, 1963. The Quitclaim deed is located at vol. 337, pp. 175-196 in the official records of Nevada County, as recorded on June 12, 1963.
Mineral rights pertain to all minerals, gas, oil and mineral deposits of every kind and nature beneath the surface of all such real property, together with all necessary and convenient rights to explore for, develop, produce, extract and take the same, subject to the express limitation that the fore-going exception and reservation shall not include any right of entry upon the surface of said land without the consent of the owner of such surface of said land, as excepted in the Quitclaim Deed recorded the 26th of January 2017 (Document #: 20170001985). Mineral rights are severed from surface rights at a depth of 200 ft (61 m) below surface, with all mineral rights being contiguous below 200 ft (61 m) of surface.
The secured loan from Eridanus Capital LLC is registered against the property by a Deed of Trust filed with the Nevada County Recorder. There are no other interests registered against or obligations required of the mineral rights of the I-M Mine Property.
Figure 4: Idaho-Maryland Mine Property, Surface and Mineral Rights
Property Access
The I-M Mine Property is situated east of the City of Grass Valley and south of Nevada City, in western Nevada County. State Route 49, State Route 20, and State Route 174 (state highways) connect the Grass Valley area regionally. The Brunswick land and the adjacent Mill Site are situated on the south western quadrant of the intersection of the East Bennett Road and Brunswick Road, a road connecting Grass Valley with State Highway 174. Access to the Brunswick land is on East Bennet Road, approximately 2.8 miles east of Grass Valley Center. The Idaho land can be accessed by Idaho Maryland Road or Centennial Drive.
Agreements
Rise owns a 100% interest in the I-M Mine Property and there are no known royalties on future gold production. The secured loan from Eridanus Capital LLC is registered against the property by a Deed of Trust filed with the Nevada County Recorder. There are no other known agreements or encumbrances to which the I-M Mine Property is subject.
Environmental Liabilities
Environmental studies have been completed on all the surface holdings owned by Rise. The environmental studies were completed prior to Rise purchasing the Idaho land and Brunswick land.
Idaho Land
In 2016, a Draft Preliminary Endangerment Assessment (PEA) report on the Idaho Land was prepared for the City of Grass Valley by Geocon Consultants Inc. This report provided conclusions and recommendations to support redevelopment of this site for commercial and industrial use. Geocon noted the metal of greatest concern with respect to potential health risks for future site occupants is arsenic which is present in mine tailings and waste berms located on the site. Geocon noted that the presence of arsenic in mine waste on the site does not currently appear to pose a significant risk to public health or the environment in its current state and that an expedited response action does not appear warranted at this time (Geocon, 2016).
On behalf of Rise Grass Valley, NV5 prepared a Draft Final Preliminary Endangerment Assessment (PEA) report that summarizes the findings of additional investigation and presents the results of risk assessment as required by the California EPA. The Draft Final PEA report was conditionally approved by the California EPA in a letter dated June 11, 2020. NV5 addressed the conditions of approval and issued the Final PEA report on June 12, 2020.
On behalf of Rise Grass Valley, NV5 prepared a Draft Remedial Action Plan (RAP, July 1, 2020)) to outline procedures for excavation, on-site transport and consolidation of mine waste as engineered fill in a 5.6-acre area on the eastern edge of the property. The RAP is based on the findings of the Final PEA and risk assessment (NV5, June 12, 2020). The RAP presents the findings of engineering evaluation, cost analysis and remedial action planning, and includes procedures for remedial implementation, verification sampling and analysis, and reporting. The 5.6-acre mine waste consolidation area will be subject to a land use covenant that restricts future disturbance of the consolidated mine waste. The mine waste consolidation area is to be covered with additional material from future mining operations that will be used to prepare the property for future commercial/industrial uses. The RAP was reviewed by Cal EPA, and approval of the Final RAP is currently in progress.
Brunswick & Mill Site Land
In 2007, a Phase I Environmental Site Assessment (ESA) for the Round-Hole and New Brunswick Mine Sites was prepared by Engineering/Remediation Resources Group, Inc. ("ERRG") for Idaho-Maryland Mining Corporation. The report concluded that there were no current recognized environmental conditions on the I-M Mine Property at the time, although there are suspect environmental concerns regarding spills of hydrocarbons from vandalism at the New Brunswick Shaft, roofing asphalt on the property, debris from illegal dumping on the property boundaries, and the potential for naturally occurring asbestos in serpentinite rocks on the property. ERRG did not complete an analysis to determine if contamination from historic mining and mineral processing was present, although ERRG has recommended further sampling and studies to determine this (ERRG, 2007).
In 2006 a Phase II Environmental Site Assessment (ESA) for the Mill Site was completed by Geomatrix Consultants Inc. for Sierra Pacific Industries, Inc. Extensive reclamation and environmental work had previously taken place on the Mill Site. There is mine waste rock on the property which has elevated arsenic levels however Geomatrix concluded that this rock is not discharging elevated metals into the local watershed. Ground water samples taken on the site as part of the ESA had residual Volatile Organic Compounds (VOC). The evaluation concluded that the residual VOC contamination presents no threat to human health from vapor migration to indoor air. The property has a deed restriction which restricts the use of groundwater for any domestic purpose and the construction of wells for the purpose of extracting water unless expressly permitted by the Regional Water Board (Geomatrix, 2006).
On behalf of Rise Grass Valley, NV5 prepared a Phase I/II ESA (June 16, 2020) presenting the results of additional investigation and addressing historical conditions identified in previous reports. Results indicated that the mine waste fill was generally less than five feet deep except at locations south of the New Brunswick Shaft and in the central-eastern portion of the property. Laboratory test results indicated that arsenic concentrations detected in mine waste samples were relatively low except for the mixed soil and rock fill located at a paved area in the southeastern portion of the property. This soil and rock fill was generally located beneath pavement and was typically less than five feet deep. This mine waste is believed to have originated from offsite rather than from the New Brunswick shaft.
Exploration Permits
All parcels included in the I-M Mine Property are within the "M1" Light Industrial Zoning District of Nevada County. Mineral exploration is allowed in M1 Districts subject to zoning compliance and building permit issuance, if required. A Use Permit is only required for mineral exploration if one of the following conditions are triggered, as per NCC § L-II 3.22(D)(2):
(a) Overburden or mineral deposits in excess of 1,000 cubic yards are disturbed, or
(b) The operation in any one location exceeds one acre in size, or
(c) Dewatering will occur or water will be discharged from the site as a result of the operation.
Additionally, all exploratory operations shall require a reclamation plan and secure adequate financial assurances to ensure site reclamation unless:
(a) Less than 1,000 cubic yards of overburden are disturbed, and
(b) The size of the operation in any one location is one acre or less.
In those instances where a reclamation plan is not required, an erosion control plan as per NCC § L-V 13.14., approved by the Nevada County Planning Department, and a grading permit shall be required for those operations in which 50 cubic yards or more of overburden are disturbed as per NCC § L-II 3.22(D)(2) (NCC, 2017).
A building permit, issued by the County, may be required for construction or installation of drilling facilities. A building permit is a ministerial approval. Ministerial approval is a non-discretionary approval.
Surface exploration drilling will be subject to Nevada County Noise Regulations. The Noise Element of the Nevada County General Plan (2014) establishes maximum allowable exterior noise levels for various land use categories (NC-BOS, 2014).
Subsurface and Surface Mining Permits
Subsurface mining is allowed in the M1 District with approval of a Use Permit. (NCC § L-II 3.21.) Approval of a Use Permit for mining operations requires a noticed public hearing before the County Planning Commission, which decision may be appealed to the County Board of Supervisors. (NCC § L-II 5.6.) Use Permit approvals include conditions of approval, which are designed to minimize the impact of conditional uses on neighboring properties.
Subsurface mining, including ancillary surface uses, would require the following permits and approvals:
County Approvals
A. Use Permit for surface and subsurface mining activities
B. Reclamation Plan for surface disturbance
C. Mitigated Negative Declaration or Environmental Impact Report in compliance with the California Environmental Quality Act ("CEQA") to analyze and mitigate environmental impacts
D. Water Well Permit by the County for the drilling of any well
E. Building Permits for construction of any structures
F. Spill Prevention Control and Countermeasures Plan for underground storage of more than 42,000 gallons of petroleum or above ground storage of more than 10,000 gallons of petroleum
The following permits and approvals may also be required depending on the configuration of the Project and the characteristics of the natural resources found in the Project-vicinity:
California Department of Fish and Wildlife ("CDFW") Approvals
G. Streambed Alteration Agreement
H. Incidental Take Permit for take of any species listed under the California Endangered Species Act ("CESA")
State Water Resources Control Board ("SWRCB") and/or Central Valley Regional Water Quality Control Board ("RWQCB") Approvals
I. National Pollution Discharge Elimination System ("NPDES") permit for discharges of stormwater
J. Report of Waste Discharge for any discharges of water from mining processes
K. Clean Water Act Section 401 Water Quality Certification from the RWQCB (only if a CWA Section 404 permit is required from the U.S. Army Corps of Engineers)
U.S. Army Corps of Engineers ("Corps")
L. Clean Water Act Section 404 permit for any discharge of dredge or fill material into the waters of the United States,
M. Environmental Assessment compliant with the National Environmental Policy Act by either the Corps or the USFWS
United States Fish and Wildlife Service ("USFWS")
N. Issuance of a Biological Opinion and Incidental Take Statement for take of any species listed under the Endangered Species Act
Northern Sierra Air Quality Management District ("AQMD")
O. Authority to Construct and Permit to Operate for any regulated air pollutant emitting sources such as diesel generators
History
The Idaho-Maryland Mine Property located in the Grass Valley mining district of northern California was one of the most productive and best-known gold mines in the Unites States, with gold production from the I-M Mine Property dating back to 1863.
The I-M Mine, as it now exists, represents a consolidation of a number of important early day producing mines including Eureka, Idaho, Maryland, Brunswick, and Union Hill Mines. Based on historic production records, the I-M Mine produced a total of 2.4 Moz of gold at an average mill head grade of approximately 0.5 oz/ton (17.1 gpt). The I-M Mine was reportedly the second largest gold mine in the United States in 1941 (Clark, 2005), producing up to 129,000 oz gold per year before being forced to shut down by the US government in 1942 (Shore, 1943). Due to lack of development, a decline in gold production was experienced and recovery from war-time shutdown never occurred.
Historic Exploration & Mine Development
The I-M Mine has a rich history of mining work completed between 1863 and 1956 by various operators. Extensive exploration and underground mine development were completed during that time on the I-M Mine Property. The I-M Mine Property and its comprehensive collection of original documents was rediscovered in 1990 by Consolidated Del Norte Ventures Inc., the predecessor company of Emgold Mining Corporation ("Emgold"), and efforts were made to reopen the historic mine.
Exploration & Mine Development 1851-1956
Exploration by historic operators from 1851 through to 1956 was mainly completed by lateral exploration (drift development) and raise or winze development. Levels were driven along the strike of the veins to determine their extent. Raises were developed upwards following the inclination of the vein and winzes were sunk down along the dip of the vein. Chip samples were assayed for mineralization of the quartz vein. In 1923, the first prospect drill was purchased. Following that, exploration holes were completed ahead of mine development to confirm vein locations and to locate vein extensions.
The I-M Mine encompasses a system of underground tunnels, many raises, numerous winzes, four inclined shafts, and two vertical shafts. An estimated equivalent of 72.8 miles (117 km) of underground tunnel occur at the I-M Mine, assuming typical drift dimensions of 7.5 ft x 8.5 ft (W x H).
Based on available historic records, 883 exploratory holes totaling approximately 234,100 ft (71,354 m) were diamond drilled at a diameter of 7/8" (EX-size). Historic drill logs were not available for review and no historic drill core was preserved from past mining operations at the I-M Mine.
Exploration & Mine Development 2003-2004
Emgold and its former entities leased the I-M Mine Property from 1990 to 2013. Development work during this period included completion of a preliminary investigation of the mine records, publishing various technical reports on the I-M Mine Property, leasing or purchasing adjacent properties, various permit applications and associated environmental studies, development of a ceramics technology process, and completion of an exploration program. Emgold was unsuccessful in reopening the historic mine due to inability to raise necessary funding in the midst of unfavourable market conditions.
Emgold completed an exploration program on the I-M Mine Property in 2003 and 2004. Gold exploration consisted of 31 diamond drill holes totaling 21,335 ft (6,502 m) and 7 drill holes totaling 3,537 ft (1,078 m) were completed for geotechnical and ceramics feedstock work.
The surface exploration drill program focused on the westernmost portion of what Emgold termed the Idaho Deformation Corridor, along the Idaho Fault Zone. Exploration drilling was mainly conducted from two sites: 1) west of the Eureka shaft and 2) west of the Idaho shaft, both targeting near surface mineralization around historic workings.
The Emgold diamond drill hole database was acquired by Rise in the purchase of the I-M Mine Property. As per the purchase agreement with the BET Group, ownership transfer of the I-M Mine Property included all historical documents to which the BET Group held rights, inclusive of Emgold data.
Production History
Rise has completed a compilation of the mine production data of the I-M Mine during historic operation from 1866 through 1955, the final year of production from the mine. Rise estimates that the I-M Mine produced a total of 2,414,000 oz of gold from 5,298,000 tons of mill feed and that the life of mine average mill head-grade averaged approximately 0.50 oz/ton (17.1 gpt). Total production for the I-M Mine is detailed in Table 3.
Table 3: Total Idaho-Maryland Mine Production from 1866-1955*
|
Mined & Milled
|
Mill Head Grade
|
Metallurgical
Recovery
|
Yield
|
Gold Produced
|
|
Tons
|
tonnes
|
oz/ton
|
gpt
|
%
|
oz/ton
|
oz
|
Idaho Mine
|
|
|
|
|
|
|
|
#1 Vein
|
978,000
|
887,000
|
1.12
|
38.6
|
85%
|
0.96
|
935,000
|
3 Vein system
|
1,215,000
|
1,102,000
|
0.60
|
20.4
|
95%
|
0.56
|
686,000
|
Total
|
2,193,000
|
1,989,000
|
0.83
|
28.4
|
89%
|
0.74
|
1,621,000
|
Brunswick Mine
|
|
|
|
|
|
|
|
Old Brunswick
|
41,000
|
37,000
|
0.56
|
19.3
|
85%
|
0.49
|
20,000
|
Union Hill
|
35,000
|
32,000
|
1.21
|
41.5
|
85%
|
1.03
|
36,000
|
|
Mined & Milled
|
Mill Head Grade
|
Metallurgical
Recovery
|
Yield
|
Gold Produced
|
|
Tons
|
tonnes
|
oz/ton
|
gpt
|
%
|
oz/ton
|
oz
|
New Brunswick
|
3,029,000
|
2,748,000
|
0.26
|
8.8
|
95%
|
0.24
|
737,000
|
Total
|
3,105,000
|
2,817,000
|
0.27
|
9.3
|
94%
|
0.26
|
793,000
|
Total I-M Mine
|
5,298,000
|
4,806,000
|
0.50
|
17.1
|
91%
|
0.46
|
2,414,000
|
*Details regarding data verification are presented under the heading "Data Verification" below.
In 1926, Errol MacBoyle took over management of the I-M Mine and, as President and General Manager, led the mine into its most successful period of production. A graph of production from the Idaho and Brunswick Mines from 1926 to 1955 is displayed in Figure 5. The historic mine workings of the I-M Mine are displayed in Figure 6.
Figure 5: I-M Mine Gold Production from 1926-1955*
Figure 6: Idaho-Maryland Mine Workings, Plan View
Mill Head Grade
The mill head grade is the grade of the mineralized material which is fed into the processing plant to be concentrated into gold bullion. The mill head grade includes mining dilution from un-mineralized rock adjacent to the veins. The mill head grade does not account for metallurgical recovery of gold during the processing of the mineralized material.
Data Verification
Detailed production information from the internal records of the I-M Mine property is available for the period from 1926 through 1955. Whenever possible, mill reports were reconciled against financial statements and submissions by Rise to the US Bureau of Mines. Where reconciliation between documents was possible, only minor variations in production reporting were noted. The entire library of documents is no longer fully complete but there is sufficient material to make an accurate estimate of historic production during this period. The following materials were used to prepare an estimate during the period from 1926-1955:
-
Idaho Maryland Mines Co. Financial Statements (1926-1932, 1934-1942)
-
Idaho Maryland Mines Co. Mill Reports (1933-1942, 1946-1950)
-
Idaho Maryland Mines Co. Final Distributions Sheets (1944, 1945)
-
Idaho Maryland Mines Co. Breakdown of Income and Expenses (1946-1949)
-
Idaho Maryland Mines Co. Cost Data & Cost Sheets from (1946-1949)
-
Idaho Maryland Mines Corp. Lode Mine Production Report to US Bureau of Mines (1944-1945, 1947-1948, 1950, 1952, 1953, 1955)
For the period prior to 1926 there are no internal corporate records regarding historic production. The following documents were used to prepare an estimate during the period from 1866-1925:
-
Lindgren, Waldemar. The Gold Quartz Veins of Nevada City and Grass Valley Districts, California (1896)
-
Hamilton, Fletcher. Mines and Mineral Resources of Nevada County (1918)
-
Clark, Jack. Gold in Quartz: The Legendary Idaho Maryland Mine (2005)
Detailed records of metallurgical recoveries from the I-M Mine prior to 1924 are also not available. From 1924-1930 gold recoveries ranged from 72% to 89% using a similar process to that used in the years prior to 1924. Lindgren (1896) estimated that gold mills in the Grass Valley mines averaged 75% metallurgical gold recovery but noted that the I-M Mine was unique in that it treated the tailings from its concentrates by secondary processes. Rise has assumed a metallurgical recovery of 85% for the pre-1924 processing at the I-M Mine which it believes is the best estimate possible given the information available.
Geological Setting, Mineralization and Deposit Types
Geology
The I-M Mine Property is located in the Grass Valley area of the Western Sierra Nevada Foothills of Northern California. This belt of rocks consists of late Paleozoic marine sedimentary and ophiolitic rocks, and early and late Mesozoic submarine volcanic-arc and basinal terranes.
The Jura-Triassic arc belt has yielded the majority of gold production in the Western Sierra Nevada Foothills. Gold deposits in Jura-Triassic arc belt are associated with second, third, and fourth-order faults related to the regionally significant Wolf Creek/Bear Mountain and Melones faults.
The Grass Valley area is dominated by blocks of variably metamorphosed volcanic, mafic plutonic, and minor sedimentary rocks hosted in a serpentinite matrix. The whole package of rocks exhibits a region foliation and is interpreted as a serpentinite-matrix tectonic mélange. These rocks were variably metamorphosed from lower greenschist to amphibolite facies during and after accretion to the continental margin. Two distinct gold vein groups exist within the Grass Valley district: steeply dipping E-W-trending veins in the northern and generally N-S trending veins with gentler dips averaging 35° in the southern part of the district. The most important E-W veins are associated with the I-M Mine Property. Both vein sets have extraordinary vertical and lateral persistence; individual veins extend for kilometers.
Mineralization
All of the significant gold production from the I-M Mine was localized within and around the Brunswick Block, which consists of variably metamorphosed volcanic and intrusive, and minor sedimentary rocks. The Brunswick Block is surrounded to the west, north, and east by gabbro and serpentinite rocks. Overlying Tertiary volcanic rocks mask rock units along the southern boundary of the Brunswick Block. The contacts between the Brunswick Block and surrounding gabbro and serpentinite are dominated by the 6-3, the Idaho, and the Morehouse Fault domains. Mineralization is closely associated with these significant second or third order structures close to the contact between the Brunswick block and serpentinite contact. Gold in the quartz veins occurs as native gold, ranging from very fine grains to large nuggets within the quartz. Sulfide minerals, primarily pyrite with lesser galena, chalcopyrite, from 1% to 4% are commonly associated with gold mineralization. Scheelite is common in the Union Hill area near the Brunswick mine. Gangue minerals include quartz, carbonate, sericite, chlorite, mariposite, and albite. Ankerite is a common alteration mineral and may occur in the mafic and ultra-mafic rocks and the meta-volcanic rocks. The mineralized wall rock is strongly carbonate altered.
Gold mineralization on the I-M Mine Property can be divided into three significant vein systems: the Idaho, the Brunswick, and the Morehouse systems.
Idaho System
The #1 Vein, #2 Vein, and 3 Vein System comprise the Idaho Vein System.
The Eureka discovery showing outcropped at the western end of the #1 Vein system but had only minor gold concentration and could not be traced on surface east or west. High grade mineralization plunging to the south east was intersected starting at approximately 100 ft (30 m) below surface at this showing. Follow-up exploration and mining led to the development of the prolific Eureka-Idaho ore shoot which plunges at approximately 30° to the south east and has a pitch length of almost 1 mile (1.6 km) and a breadth of 500 ft to 1,000 ft (152 m to 305 m). The width of the vein within the ore shoot averaged approximately 3 ft (~1 m) and in places ranged up to 8 ft (~2.4 m). The average insitu grade of the #1 Vein would likely have been slightly higher than the estimated mill head grade of 1.12 oz/ton (39 gpt). The trend of the shoot is approximately parallel to an expected trend of the intersection of the Idaho and Morehouse faults suggesting the interaction of the Idaho and Morehouse faults may have played a role on the formation of the rich mineralization encountered in the Eureka-Idaho stope. Alternatively, the shape of the Brunswick Block may have influenced this trend.
The Idaho #1 Vein occurs coincident with a diabase dike hosted in ankerite, in close proximity to the serpentinite-Brunswick Block contact. Just west of the Idaho shaft, at the western end of the Idaho #1 Vein, the diabase dike bends in an arc to the south mimicking a fold around the nose of the Brunswick Block. The Eureka-Idaho ore shoot pinches out at the I1500 Level but significant gold grades coincident with a diabase dike hosted in serpentinite in close proximity to the serpentinite-Brunswick contact were exposed in workings on the I2400 Level suggesting the vein may open up again or a second vein is present. To the east, the Eureka-Idaho ore shoot pinches out near the #2 Vein. All rocks are highly altered and contain much ankerite. The cross section in Figure 7 shows the general form and relationship of the #1 Vein with the serpentinite and diabase dike.
Figure 7: #1 Vein Cross Section, Section looking East (Lindgren, 1896)
The #2 Vein is a disrupted zone of quartz veins trending northeast and dipping steeply to the south east. This vein system is hosted in the serpentinite approximately coincident with where the serpentinite-Brunswick Block contact bends abruptly to the north before turning east again. #2 Vein trends northeast into the 3 Vein System.
The 3 Vein System, like the #1 Vein system, hosts a prolific ore shoot. The 3 Vein System comprises an Idaho fault split into four main branches. Connecting diagonal structures between the four fault branches were also mineralized. As with the #1 Vein, gold mineralization is associated with a diabase dike sub parallel to the serpentine-Brunswick Block contact. The main 3 Vein was mined continuously over a vertical distance of approximately 1,500 ft (457 m) and an average horizontal strike length of approximately 700 ft (213 m). There were several important veins which splayed from the main 3 Vein, forming the larger 3 Vein System. The most important of which were named the 5 Vein, 13 Vein, and 22 Vein. Minor splays from the main 3 Vein included 19 Vein, 4 Vein, and 6 Vein. The 3 Vein ranged in dip from 45° to 70°, with an average dip of approximately 55°. An average vein width of approximately 5 ft (1.5 m) was typical but in places reached widths of over 20 ft (6 m).
In the 3 Vein System, the best mineralization was typically found in quartz veins where the Idaho structures intersected areas where diabase dikes or Brunswick Block rocks are in contact with the serpentinite unit. Veins hosted solely in serpentinite were rarely of economic importance due to the ductile nature of the serpentinite which typically does not allow wide or continuous open structures to form from faulting. The 23 Vein is an exception. Also known as the Rose Garden, it was intersected by exploration drifting 2,000 ft (610 m) east of the main 3 Vein System on I2000 Level. The mine operator was following the Idaho #5 Vein towards the 6-3 Fault and located the 23 Vein by diamond drilling. The 23 Vein dips to the northwest as opposed to the southwest and is hosted entirely in ankerite/serpentinite. It is quite narrow but was noted to contain abundant visible gold. The 23 Vein was followed along strike to the southeast directly to its intersection with the 6-3 Fault.
Brunswick System
The Brunswick vein system constitutes a distinct vein system within meta-volcanic rocks of the Brunswick Block. The veins strike northwesterly and have a southwesterly dip. These parallel, vertically dipping mineralized veins were mined above 1600L along continuous strike lengths ranging from 430 ft (131 m) to 1,000 ft (305 m) with continuous vertical heights reaching up to 1,000 ft (305 m). These veins generally range from several inches up to 8 ft (2.4 m) in width. A few veins with opposite strike and dip occur. The veins are most numerous and have the highest grades near the 6-3 Fault. The veins nearest to the fault turn to the north on the footwall side, suggesting a northward component of movement of the hanging wall. A quartz-carbonate stockwork develops near the fault. The quartz stringers dip from the veins toward the fault and many have connecting diagonals extending from an upper to a lower stringer toward the fault. The Brunswick veins generally pinch out before rarely coming in contact with the fault footwall. No significant mineralization is present in the fault. Only a few unimportant veins are known beyond its hanging wall.
In the area of the Brunswick veins there are layers of meta-sedimentary rocks within the meta-volcanic rocks that exhibit the regional N-W schistosity dipping very steeply to the north. Where the Brunswick veins cross these meta-sedimentary rocks vein splitting and en-echelon crossings occur forming what is known in the historical records as "Zebra Rock." The "Zebra Rock" produced "fair" to "good" grades of large tonnage and the presence of free gold was reported. A large "Zebra Rock" zone was intersected and mined along the western extents of 16 Vein from levels 1300L to 1000L. Mining in this zone occurred over strike lengths from 360 ft to 525 ft (110 m to 160 m) and reached widths of up to 110 ft (34 m) on 1100 level.
Morehouse System
The Morehouse vein system is not as well understood as the Idaho #1, #2, 3 Vein System, and Brunswick vein systems. It is defined by fault and quartz-vein and quartz stockwork intersections in workings and drill holes in only a few areas such as the Morehouse, 16 Vein, 52 Vein, and 60 Winze. There is little historic production from the Morehouse Vein system.
The Morehouse vein is associated with the serpentinite-hosted diabase dike wrapping around the western end of the Brunswick Block. Underground working show the Morehouse connects directly to the Idaho #1 Vein. The extension of the Idaho shaft in 1923 to I1500 Level intersected the Morehouse splay and the shaft station on I1500 Level is right above the #1 Vein.
The best Morehouse mineralization intersected to date, and the only significant production, occurs within the Brunswick Block at the 52 Vein and 60 Winze areas. There is very little other exploration of this vein in the Brunswick Block.
Mineral Deposit Type
The Idaho System deposits on the I-M Mine Property can be described as an orogenic gold deposit. Orogenic gold deposits encompass a broad range of depth of formation and different host lithologies; however, common to orogenic gold deposits is a spatial association with compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens. Most ores are post-orogenic with respect to tectonism of their immediate host rocks but are simultaneously syn-orogenic with respect to ongoing deep-crustal, subduction-related thermal gradient. Depth of formation of orogenic deposits are best subdivided into epizonal (<6 km / <3.7 mi), mesozonal (6-12 km / 3.7-7.5 mi), and hypozonal (>12 km / >7.5 mi).
The gold deposits on the I-M Mine Property have been classified as Mesothermal Quartz Veins (Lindgren, 1894), are also known as and are type-examples of low-sulfide Au-quartz vein deposits (Berger, 1986), and gold quartz vein deposits (Ash, 2001). These classifications are sub-groups of orogenic gold deposit type.
Exploration
Rise has completed an exploration drilling program on the I-M Mine Property in June of 2019. Up to July 31, 2019, Rise has completed seventeen drill holes, B-17-01, B-18-02 thru B-18-07, Z-18-08 & Z-18-09, I-18-10-I-18-12, I-19-13, I-1913A, I-19-12A, I-19-12B, I-19-14, & I-19-14A. Total drilling completed to July 31, 2019 by Rise Gold is ~20,584 meters. Assay results for all drill holes have been released as of July 31, 2019.
Exploration drilling at the Brunswick portion of the Idaho-Maryland Gold project has been successful with numerous gold-bearing veins intersected and previously released in 2018 on January 3rd, June 28th, July 23rd, August 7th and December 13th and in 2019 on March 19, May 21st, and June 28th, 2019. A summary of drill highlights for the program released through July 31th, 2019 is presented in the table.
Drill Intercept Highlights Released to July 30th 2019
|
Hole
|
From
(m)
|
To (m)
|
Gold
(gpt)
|
Intercept
Length
(m)
|
Estimated
True
Width
(m)
|
Vein
|
B-17-01
|
638.89
|
653.80
|
12.2
|
14.90
|
7.8
|
B1
|
Including
|
643.74
|
646.48
|
62.7
|
2.74
|
|
B1 Center
|
Including
|
644.96
|
645.57
|
266.0
|
0.61
|
|
|
B-17-01
|
1111.61
|
1126.85
|
4.5
|
15.24
|
?
|
?
|
Including
|
1112.06
|
1113.59
|
40.6
|
1.52
|
|
|
B-18-02
|
578.42
|
582.78
|
7.9
|
4.36
|
1.0 - 3.4
|
B116 or B1
|
B-18-03
|
516.64
|
518.62
|
6.0
|
1.98
|
1.7
|
B1 East
|
B-18-04
|
516.94
|
520.96
|
8.0
|
4.02
|
3.0
|
B32
|
Including
|
516.94
|
518.01
|
23.0
|
1.07
|
|
|
B-18-04
|
625.27
|
628.04
|
4.0
|
2.77
|
2.1
|
B10 HW
|
B-18-04
|
637.03
|
640.08
|
4.4
|
3.05
|
2.3
|
B10 FW
|
B-18-04
|
711.92
|
715.21
|
5.1
|
3.29
|
1.8
|
B18
|
B-18-05
|
667.88
|
671.38
|
5.9
|
3.51
|
2.0
|
B10 HW
|
Including
|
670.32
|
671.38
|
13.0
|
1.07
|
|
|
B-18-05
|
682.90
|
690.37
|
2.4
|
7.47
|
4.1
|
B10 FW
|
B-18-05
|
748.28
|
763.58
|
2.6
|
15.30
|
11.0
|
B41
|
B-18-05
|
899.59
|
905.53
|
2.5
|
5.94
|
3.4
|
B39
|
B-18-05
|
978.10
|
983.28
|
22.4
|
5.18
|
2.6
|
B40
|
Including
|
978.10
|
979.32
|
93.2
|
1.22
|
|
|
B-18-05
|
1590.14
|
1594.56
|
23.7
|
4.42
|
3.2
|
IB30
|
Including
|
1593.59
|
1594.01
|
230.0
|
0.43
|
|
|
B-18-05
|
1887.47
|
1890.43
|
10.9
|
2.96
|
2.0
|
IB50
|
Including
|
1889.36
|
1889.85
|
61.0
|
0.49
|
|
|
B-18-06
|
682.75
|
688.54
|
2.6
|
5.79
|
4.1
|
B10
|
B-18-06
|
766.54
|
775.50
|
4.9
|
8.96
|
8.2
|
B41
|
B-18-07
|
733.35
|
736.40
|
3.0
|
3.05
|
2.4
|
B6
|
B-18-07
|
746.49
|
750.14
|
4.0
|
3.66
|
2.8
|
B10 HW
|
B-18-07
|
756.97
|
760.78
|
1.9
|
3.81
|
5.4
|
B10 FW
|
Z-18-08
|
No Significant Intercepts
|
|
|
|
Z-18-09
|
309.68
|
316.38
|
3.3
|
6.71
|
?
|
Zebra
|
I-18-10
|
171.08
|
174.60
|
4.7
|
3.52
|
?
|
Zebra
|
I-18-10
|
958.02
|
965.61
|
1.8
|
7.59
|
?
|
52 HW
|
I-18-10
|
965.61
|
972.01
|
3.2
|
6.40
|
?
|
52
|
I-18-10
|
977.98
|
978.44
|
97.3
|
0.46
|
?
|
52 FW
|
I-18-10
|
987.77
|
994.58
|
149.3
|
6.81
|
?
|
52 FW
|
Including
|
993.42
|
993.88
|
2190.0
|
0.46
|
|
|
I-18-11
|
259.16
|
262.04
|
8.5
|
2.88
|
?
|
?
|
Including
|
261.14
|
262.04
|
18.8
|
0.90
|
|
|
I-18-11
|
975.50
|
976.70
|
19.2
|
1.20
|
?
|
52
|
I-18-11
|
992.25
|
993.88
|
15.4
|
1.63
|
?
|
52
|
Including
|
992.70
|
993.22
|
35.6
|
0.52
|
|
|
I-18-11
|
1046.17
|
1052.58
|
3.9
|
6.42
|
?
|
52
|
I-18-11
|
1142.33
|
1144.08
|
5.4
|
1.75
|
?
|
52
|
I-18-11
|
1381.86
|
1384.33
|
3.6
|
2.47
|
?
|
I1
|
I-18-12
|
950.50
|
960.49
|
2.6
|
9.98
|
?
|
|
I-19-12B
|
1367.27
|
1373.22
|
9.4
|
5.94
|
?
|
I1
|
Including
|
1367.27
|
1370.11
|
18.5
|
2.83
|
?
|
I1
|
Including
|
1369.04
|
1370.11
|
46.3
|
1.07
|
?
|
I1
|
Including
|
1369.74
|
1370.11
|
111.5
|
0.37
|
?
|
I1
|
I-19-13
|
1007.97
|
1013.09
|
5.5
|
5.12
|
?
|
I1
|
I-19-13A
|
1005.31
|
1009.57
|
90.4
|
4.27
|
?
|
I1
|
Including
|
1008.77
|
1009.57
|
458.0
|
0.81
|
|
|
I-19-14A
|
1014.42
|
1029.31
|
1.4
|
14.9
|
13.59
|
I2
|
Including
|
1014.42
|
1016.36
|
6.2
|
1.9
|
1.77
|
I2
|
Rise has prepared a drill hole database derived from information contained in the collection of historic documents and records acquired through the purchase of the I-M Mine Property. The drill hole database is divided into I-M Mine drilling completed before the mine shut down in 1956 and Emgold drilling completed in 2004.
Sampling, Analysis and Data Verification
Sample Preparation and Analysis
Rise Gold has implemented a quality control program for our drill program to ensure best practices in the sampling and analysis of the drill core. This includes the insertion of blind blanks, duplicates, and certified standards. HQ- and NQ-sized drill core is saw cut with half of the drill core sampled at intervals based on geological criteria including lithology, visual mineralization, and alteration. The remaining half of the core is stored on-site at our warehouse in Grass Valley, California. Drill core samples are transported in sealed bags to ALS Minerals analytical assay lab in Reno, Nevada.
All gold assays were obtained using a method of screen fire assaying. The historic I-M Mine project is known to contain 'coarse' gold, for which a screen fire assay is the best way to obtain a definitive result. This procedure involves screening a large, pulverized sample of up to 1 kg at 100 microns. The entire oversize (including the disposable screen) is fire assayed as this contains the 'coarse' gold and a duplicate determination is made on the 'minus' 100-micron fraction. A calculation can then be made to determine the total weight of gold in the sample. Any +100-micron material remaining on the screen is retained and analyzed in its entirety by fire assay with gravimetric finish and reported as the Au (+) fraction result. The -100-micron fraction is homogenized and two sub-samples of 50 grams are analyzed by fire assay with AAS finish. If the grade of the material exceeds 10 gpt the sample is re-assayed using a gravimetric finish. The average of the two results is taken and reported as the Au (-) fraction result. All three values are used in calculating the combined gold content of the plus and minus fractions.
There is no detailed information describing sample preparation, analysis and security procedures applied by mine operators prior to 2002. The historical samples were reportedly fire-assayed at former mine site laboratories. No records exist of any QA/QC program.
Emgold sample preparation, analysis and security procedures for core collected by Emgold are described in a 2009 Technical Report prepared by Robert Pease, P.G., for Emgold titled "Idaho-Maryland Mine Project, Grass Valley CA". Three-foot core samples were cut in half by a wet saw. The half core samples were put in a sample bag, tagged, and shipped to a laboratory. All samples were crushed to 80% passing -10 mesh, rotary split to a 500 g subsample which was pulverized to 95% passing -150 mesh. All samples were analyzed using screened metallics fire assay methods. The QAQC program used Standard Reference Materials, blank samples, coarse reject and pulp duplicate samples, and third-party laboratory check assays. Insertion rate of SRMs and duplicates was approximately 1 in 20 samples. Blanks were only inserted immediately following mineralized intervals. The control samples were reportedly used to successfully control the assay quality process.
Historical Data Verification
Although Rise has carefully digitized and checked the locations and values of drill hole results from level plans and other documents, the absence of drill hole related documentation, such as drill logs, drill hole deviation, core recovery and density measurements, assay certificates, and possible channel sample grade biases, could materially impact the accuracy and reliability of the reported results.
Mineral Processing and Metallurgical Testing
Rise has conducted mineral processing and metallurgical testing analyses on recent drill core from the I-M Mine Property for the purpose of environmental study in conjunction with permitting efforts.
A significant amount of production has occurred on the I-M Mine Property which confirms that gold can be recovered, mainly by gravity and flotation methods. Nearly all gold at the I-M Mine is free milling, as demonstrated by cyanide leaching of concentrates and tailings by the I-M Mine during past production.
Mineral Resource and Mineral Reserve Estimates
No estimates of mineral resources have been prepared for the I-M Mine Property. We are not treating historical mineral resource estimated as a current mineral resource estimate. In addition, there are no mineral reserves estimates for the I-M Mine Project.
References
American Society for Testing Materials (ASTM). (2013). ASTM E1527-13, Standard Practice for Environmental Site Assessments: Phase 1 Environmental Site Assessment Process. ASTM International, West Conshohocken, PA. Retrieved at http://www.astm.org/cgi-bin/resolver.cgi?E1527-13
Ash, Chris. (June 2001). Bulletin 108: Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera. Chapter 8. Geological Survey Branch. Victoria, BC. Retrieved at http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/BulletinInformation/BulletinsAfter1940/Pages/Bulletin108.aspx
California Department of Conservation (CDC). (April 2017). SMARA Mines - AB 3098 List, Listing as of April 7, 2017). Retrieved at http://www.conservation.ca.gov/dmr/SMARA%20Mines/ab_3098_list/Pages/Index.aspx
Cal. Pub. Res. Code (CPRC). California Public Resources Code. Chapter 9 - Surface Mining and Reclamation Act of 1975. 1975.
Cal. Pub. Res. Code (CPRC). California Public Resources Code. Division 13 - Environmental Quality. 1979.
California Environmental Quality Act (CEQA). (February 1992). City of Sacramento v. State Water Resources Control Board. Retrieved at http://resources.ca.gov/ceqa/cases/1992/sac_swrcb.html
City of Grass Valley Community Development Dept. (CoGV-CDD). City of Grass Valley 2020 General Plan Map. Grass Valley, CA. November 2009.
Clark, Jack. Gold In Quartz - The Legendary Idaho Maryland Mine. Grass Valley, CA. 2005.
Engineering/Remediation Resources Group, Inc. (ERRG). Phase 1 Environmental Site Assessment Round-Hole and New Brunswick Mine Sites. Concord, CA. March 2007.
Geocon Consultants, Inc. (Geocon). Draft Preliminary Endangerment Assessment Report. Rancho Cordova, CA. August 2016.
Geomatrix Consultants Inc. (Geomatrix). Summary - Phase II Investigation: Data Collection and Analysis, Brunswick Lumber Mill Site Nevada County, CA. September 2006.
Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F. Orogenic gold deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geol. Rev. Special Issue, 13, 7-27. 1998.
Kleinschmidt. City of Grass Valley Sphere of Influence Plan. Prepared for Nevada Local Agency Formation Commission (LAFCo). April 2011.
Lindgren, W. US Geological Survey Grass Valley Special Map. 1894.
Lindgren, Waldemar. The Gold Quartz Veins of Nevada City and Grass Valley Districts, California (1896).
Nevada County Code (NCC). (March 2017). Article 3 Specific Land Uses. Retrieved from http://qcode.us/codes/nevadacounty/?view=desktop&topic=3-ii-2-l__2
Pease, Robert C. Idaho-Maryland Mine Project, Grass Valley CA Technical Report. December 2009.
Shore, F.M for United States Bureau of Mines. Mineral Yearbook 1941. Pg. 252. Washington, D.C. 1943. Retrieved at http://digital.library.wisc.edu/1711.dl/EcoNatRes.MinYB1941