TORONTO, April 23, 2020 /PRNewswire/ - Nighthawk Gold
Corp. ("Nighthawk" or the "Company") (TSX: NHK;
OTCQX: MIMZF) is pleased to provide an update of the latest
heap leach testwork from ongoing preliminary metallurgical studies
on the Colomac Gold Project ("Colomac"). Four (4) bulk drill
core samples collected in 2018 were previously submitted for
SAGDesign, gravity concentration, flotation, bottle roll cyanide
leaching, and column heap leach testing. Standard metallurgical
test results for those samples were reported earlier (see press
release dated March 19, 2019) and are
referenced in this release which covers the 2018 bottle roll and
column heap leach testwork findings.
Dr. Michael Byron, President
& CEO commented, "Metallurgical studies completed to-date
have continued to show that Colomac rock performs exceptionally
well in terms of its grind characteristics, gold recoveries,
purity, and responsiveness to all standard gold recovery
technologies. Although our ongoing heap leach bottle roll and
column tests are still at a preliminary stage, results show a
favourable response to the deposit's heap leach potential.
"Standard metallurgical testing on four Colomac 2019 samples is
almost complete. Additional heap leach testwork is also underway,
which will then give us a total of ten bottle roll and nine column
leach tests and will shed considerable insight into the ongoing
assessment of the deposit's heap leach and primary processing
potential."
Testwork Highlights:
- Testing to-date has shown that Colomac rock is amenable to all
standard gold recovery technologies including, flotation, gravity
separation, and heap leaching.
- Minimal variation in rock hardness is noted for all test
samples indicating a relatively homogeneous host rock across both
sills.
- Utilising a combination of gravity and cyanide leach recovery
processes, testing has shown that gold recoveries for all samples
tested to-date when ground to a size of 80% passing 106 microns,
range from 96.3% to 98.0%.
- Current column leach tests on the four 2018 samples posted gold
recoveries that varied from 54.9% to 69.7% and averaging 59.4% for
the 206 day run, representing an average increase of 9.6% in
recoveries when the leach time was extended for an additional 3
months (~100 additional days)(Table 2).
- Current bottle roll leach tests on four samples (minus half (½)
inch crushed material ran for 10 days) posted gold recoveries
between 31.5% and 49.6% with an average gold recovery of 44.3%.
Samples of lower-grade and higher-grade material collected in 2016
and 2017 returned recoveries of 81.8% and 57.5% respectively (see
press release dated May 22,
2018).
- Cyanide heap leach results show considerable variability
between testing methods and grade of material processed but fall
within an expected performance range for crushed material
(recoveries between 31.5% up to 81.8% in all samples tested
to-date).
Metallurgical Testwork
Testing was completed at Bureau Veritas in Richmond, BC, and audited by Starkey &
Associates Inc., in Oakville,
Ontario. Studies completed to-date include the four latest
2018 composite samples (standard testing, four bottle roll and four
column leach tests), one higher grade sample (standard testing, two
bottle roll and one column leach tests) from Zone 1.5 (see press
releases dated February 21, 2018 and
May 22, 2018), and lower-grade
material (standard testing and one bottle roll leach test)
consisting of three composite samples from various areas of the
Colomac Main Sill (see press release dated April 19, 2017).
The 2018 campaign broadened sampling (21 boreholes covering
seven (7) mineralized zones within the Colomac Main and Goldcrest
sills), to other areas of the deposit including Zones 1.0, 2.0-2.5,
3.0-3.5 and Goldcrest North (Table 1, Figure 1). The testwork
program was identical to previous campaigns, with each sample
consisting of approximately 70 kg of drill core material collected
from the respective zones. As in the previous studies, samples were
assayed for gold and tested for grindability using the SAGDesign
methodology, and for amenability to several gold recovery processes
(see press release dated March 19,
2019). For illustrative purposes, a comparison of the latest
heap leach test results to previously reported 2017 metallurgical
testing is presented in Table 3.
Calculated head grades from the various tests show that Colomac
material has a pronounced nugget effect in most samples studied
to-date. Fire assay results are consistently low while metallic
assays and screen analysis assays of all the size fractions gives a
much better indication of the amount of gold present. This is
confirmed given the extent to which gold is recovered in the tests
completed (Table 1). As expected for material with gold nuggets,
the calculated heads for various tests are erratic.
Heap Leach Testwork
The first heap leach test conducted was a bottle roll leach test on
a composite sample of Colomac Main sill lower-grade material from
the initial 2016 sampling program. It returned a highly favourable
gold recovery of 81.8%, prompting additional heap leach testing to
ascertain the opportunity for the use of heap leach recovery
methods at Colomac. To date, four bottle rolls and five column
leach tests have now been completed on minus half (½) inch crushed
material.
An initial single high-grade sample (from the 2017 sampling
program) reported a column leach test recovery of 34.3% after
leaching for 107 days (see press release dated May 22, 2018). Considering the additional results
now available, it appears that the previous low result, being the
first column test done by the Company may have had insufficient
cyanide added to the column test, which due to its high-grade
nature, probably had more cyanicides (a substance that attacks or
destroys the cyanide salt being used to dissolve precious metals)
in it than the lower-grade samples.
Current column leach tests on the four samples posted gold
recoveries that varied from 45.6% to 61.1% and averaged 49.8% for
the 107-day run. Extending the leach time for an additional 3
months (~100 more days) resulted in an average increase of 9.6%
with gold recoveries varying from 54.9% to 69.7% and averaging
59.4% (Table 2).
Bottle roll leach tests on the four samples ran for 10 days and
posted gold recoveries between 31.5% and 49.6% with an average gold
recovery of 44.3%. Samples of lower-grade and higher-grade material
collected in 2016 and 2017 returned recoveries of 81.8% and 57.5%
respectively (see press release dated May
22, 2018).
Gold recoveries from the 2018 column leaching (107 days), when
compared with the bottle roll tests, were significantly higher for
Zone 1.0 and Goldcrest North but showed similar gold recoveries for
Zones 2.0-2.5 and Zones 3.0-3.5 (Table 3). Therefore, the bottle
roll tests seem to give a rough indication of the recovery that can
be achieved but not the cyanide consumption (which is high due to
the high agitation levels used).
Results from the current study, as well as studies completed on
2017 sampling are summarized in the tables below and show that the
materials tested respond favourably to the proposed process
options.
Table 1. Head Assays of Samples Tested Using
Column Leach
Sample
ID
|
Zone
|
Au Grade,
g/mt
|
Fire
Assay
|
Metallics
|
Screen
Analysis
|
Average*
|
2018 Sample
1
|
1.0
|
1.67
|
2.28
|
3.77
|
2.57
|
2018 Sample
2
|
2.0-2.5
|
2.15
|
2.05
|
2.29
|
2.16
|
2018 Sample
3
|
3.0-3.5
|
2.38
|
2.41
|
2.81
|
2.53
|
2018 Sample
4
|
Goldcrest
|
1.34
|
2.29
|
1.48
|
1.71
|
Average
2018
|
1.88
|
2.26
|
2.59
|
2.24
|
2017
High-Grade
|
2.83
|
7.16
|
Assay not
done**
|
4.99
|
* Note: Average value
is calculated as the average of the three determinations
|
** Screen analysis
assay was added to the 2018 samples because of the nugget
effect
|
Table 2. Column Leach Tests at Minus ½ Inch
Sample
ID
|
Leach
|
P80
Size
|
NaCN
|
Measured
|
Calc.
Head
|
Recovery
|
Residue
|
Days
|
inch
|
g/L
|
Au,
g/t
|
Au,
g/t
|
Au,
%
|
Au,
g/t
|
2018 Sample
1
|
107
|
0.5
|
0.5
|
2.57
|
1.66
|
45.6
|
0.76
|
206
|
0.5
|
0.5
|
2.57
|
1.66
|
57.4
|
2018 Sample
2
|
107
|
0.5
|
0.5
|
2.16
|
2.71
|
46.4
|
1.34
|
213
|
0.5
|
0.5
|
2.16
|
2.71
|
55.5
|
2018 Sample
3
|
107
|
0.5
|
0.5
|
2.53
|
2.54
|
46.1
|
1.24
|
213
|
0.5
|
0.5
|
2.53
|
2.54
|
54.9
|
2018 Sample
4
(Goldcrest)
|
107
|
0.5
|
0.5
|
1.71
|
1.02
|
61.1
|
0.35
|
206
|
0.5
|
0.5
|
1.71
|
1.02
|
69.7
|
2018 Average after
~107 days (3.5 months)
|
2.24
|
1.98
|
49.8
|
0.92
|
2018 Average after
~210 days (7 months)
|
2.24
|
1.98
|
59.4
|
2017
High-Grade
|
107
|
0,5
|
0.5
|
4.99
|
4.70
|
34.3
|
3.15
|
Table 3. Bottle Roll & Column Leaching
Results (compared to other methods of gold recovery)
Test
|
Description
|
Particle
|
Au Recovery
(%)
|
Size
|
Samples
Tested
|
~P80
|
2017
|
2018
|
2018
|
2018
|
2018
|
2018
|
High
|
Zone
|
Zone
|
Zone
|
Goldcrest
|
Average
|
(Microns)
|
Grade
|
1.0
|
2.0-
2.5
|
3.0-
3.5
|
|
Crushed
Leach
(1/2")
|
Bottle
Roll
(10
days)
|
12700
|
57.5
|
31.5
|
49.1
|
47.1
|
49.6
|
44.3
|
Column
(~107
days)
|
12700
|
34.30*
|
45.6
|
46.4
|
46.1
|
61.1
|
49.8
|
**Column
(~210
days)
|
12700
|
N/A
|
57.4
|
55.5
|
54.9
|
69.7
|
59.4
|
Ground
Leach
|
Whole
Ore
|
150
|
96.4
|
97.1
|
96.8
|
96.7
|
96.8
|
96.9
|
Gravity +
Leach
|
106
|
98.0
|
98.0
|
97.3
|
96.3
|
97.2
|
97.2
|
***Gravity
Pan
Cl.
Conc.
|
Fine
|
75
|
54.3
|
53.0
|
42.0
|
27.2
|
58.3
|
45.1
|
Medium
|
106
|
40.5
|
48.2
|
48.8
|
24.5
|
44.4
|
41.5
|
Coarse
|
150
|
42.8
|
34.4
|
34.1
|
20.4
|
52.0
|
35.2
|
Flotation
|
Fine
|
75
|
94.6
|
94.9
|
94.8
|
92.1
|
98.1
|
95.0
|
Medium
|
106
|
93.5
|
94.5
|
94.5
|
88.6
|
94.9
|
93.1
|
Coarse
|
150
|
90.7
|
92.8
|
94.2
|
84.8
|
95.5
|
91.9
|
* Low recovery after
107 days probably due to low cyanide (high grade sample). 1.3 kg/t
Vs 4.06 kg/t for the bottle roll test.
|
** Column leach time
was extended after 107 days for the 2018 samples to study effect on
recovery of longer leach times.
|
*** The gold recovery
shown is the pan (cleaner) concentrate after panning of the gravity
rougher concentrate. Average gold rougher
recovery was 70.5% to gravity rougher concentrates in 3.4% of feed
mass for 2018 samples.
|
Future Testing
Preliminary testwork indicates that the Colomac deposit is
amenable to all standard recovery technologies. Future studies will
be broadened to include samples from other satellite gold zones and
other zones to depth within the mineralized sills. Future work will
also continue scrutinizing the heap leach potential of the Colomac
deposit. The main objective is to confirm that the metallurgical
responses observed so far will apply over a broader range of head
grades, zone locations, and depths within the deposit.
Quality Control and Qualified Persons
The technical information disclosed herein was prepared under
the supervision of Dr. Alice Shi of
Bureau Veritas and Mr. John Starkey
of Starkey & Associates Inc., who is considered an independent
"Qualified Person" as defined by NI 43-101 for the metallurgical
testing performed on behalf of Nighthawk Gold Corp. Mr. Starkey has
supervised the metallurgical work reported on and has reviewed and
approved the technical disclosure contained in this news release
with respect to such work.
Dr. Michael J. Byron, Ph.D.,
P.Geo., President & Chief Executive Officer of Nighthawk, who
is the "Qualified Person" as defined by NI 43-101 for this project,
has reviewed and approved of the technical disclosure contained in
this news release. Please refer to NI 43-101 technical report
"Technical Report and mineral resource estimate update on the
Colomac Project of the Indin Lake Property", dated June 13, 2018, as filed under the company's
profile on www.sedar.com
About Nighthawk
Nighthawk is a Canadian-based gold exploration company with 100%
ownership of a district-scale land position within the Indin Lake
Greenstone Belt, located approximately 200 km north of Yellowknife, Northwest Territories, Canada.
Nighthawk is focused on advancing the Colomac Gold Project with a
current inferred resource of 2.6 million ounces of gold (50.3
million tonnes at an average grade of 1.62 grams per tonne gold),
as well as advancing its other regional gold deposits and showings
within this largely underexplored Archean gold camp.
The Company has an experienced and dedicated team and is well
funded to complete its goals and objectives over the next 12
months.
The Toronto Stock Exchange has neither reviewed nor accepts
responsibility for the adequacy or accuracy of this news
release.
Forward-Looking Information
This news release contains "forward-looking information" within
the meaning of applicable Canadian securities legislation.
Forward-looking information includes, but is not limited to,
information with respect to the Company's continued metallurgical
testing at Colomac and the timing and results thereof. Generally,
forward-looking information can be identified by the use of
forward-looking terminology such as "plans", "expects", or "does
not expect", "is expected", "budget", "scheduled", "estimates",
"forecasts", "intends", "anticipates", or "does not anticipate", or
"believes" or variations of such words and phrases or state that
certain actions, events or results "may", "could", "would",
"might", or "will be taken", "occur", or "be achieved".
Forward-looking information is based on the opinions and
estimates of management at the date the information is made, and is
based on a number of assumptions and is subject to known and
unknown risks, uncertainties and other factors that may cause the
actual results, level of activity, performance or achievements of
Nighthawk to be materially different from those expressed or
implied by such forward-looking information, including risks
associated with the exploration, development and mining such as
economic factors as they effect exploration, future commodity
prices, changes in foreign exchange and interest rates, actual
results of current exploration activities, government regulation,
political or economic developments, environmental risks, permitting
timelines, capital expenditures, operating or technical
difficulties in connection with development activities, employee
relations, the speculative nature of gold exploration and
development, including the risks of diminishing quantities of
grades of reserves, contests over title to properties, and changes
in project parameters as plans continue to be refined as well as
those risk factors discussed in Nighthawk's annual information form
for the year ended December 31, 2018,
available on www.sedar.com. Although Nighthawk has attempted
to identify important factors that could cause actual results to
differ materially from those contained in forward-looking
information, there may be other factors that cause results not to
be as anticipated, estimated or intended. There can be no assurance
that such information will prove to be accurate, as actual results
and future events could differ materially from those anticipated in
such information. Accordingly, readers should not place undue
reliance on forward-looking information. Nighthawk does not
undertake to update any forward-looking information, except in
accordance with applicable securities laws.
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SOURCE Nighthawk Gold Corp.