Dong Mao Huo Project
October 14 2008 - 2:15AM
UK Regulatory
Central China Goldfields plc
("GGG" or "the Company")
DONG MAO HUO PROJECT
INITIAL METALLURGICAL RESULTS
LONDON - 14 October 2008
Central China Goldfields plc (AIM: GGG) is pleased to announce that
the Company has received the initial results from the preliminary
metallurgical tests of the Dong Mao Huo oxide and sulphide ores.
Highlights:
- Column test of the oxide ore at 1 inch size yields 90% gold
recovery in 16 days suggesting that the ore will leach well in a heap
leach.
- Sulphide ore achieved 97-99% gold recovery, 97-99% silver recovery
and 95-97% copper recovery in the rougher by flotation method.
- Leaching of sulphide ore achieved 79.7-81.4% gold recovery.
Jeff Malaihollo, Managing Director of Central China Goldfields plc,
comments:
"These initial metallurgical tests indicate relatively simple
metallurgy with the oxide ore amenable to low-cost heap leach processing. The
best processing route for sulphide ore is still being investigated."
Technical Details:
Three types of ores were submitted for metallurgical testing, these
are composite oxide ore at about 1.17 gramme per tonne gold ("g/t Au"), 2.83
g/t silver ("Ag") and 0.04% copper ("Cu") head grade coming from the East Hill
zone; composite low-grade sulphide ore at about 1.02 g/t Au, 6.1 g/t Ag and
0.17% Cu and composite high-grade sulphide ore at about 3.51 g/t Au, 27.6 g/t
Ag and 0.56% Cu head grade from diamond drill cores representing the West Hill
zone. The tests were conducted by the Process Research Associates (PRA) Group
of Companies of Vancouver, Canada (now part of Inspectorate) and supervised by
Peter Tse.
Oxide Ore:
Agitated coarse cyanide leach tests for 7 days of leaching were
conducted on the composite oxide ore at 1, � and � inch sizes as shown in
Table 1.
Table 1. Summary of coarse cyanide leach test results on the oxide
ore sample
Ore Type Crush Time Head % Au kg/T NaCN kg/T
(days) Extraction Usage Ca(OH)2
Size g/t Au Usage
Oxide 1/4 inch 7 0.94 95.7 1.06 0.24
1/2 inch 7 0.94 95.7 0.96 0.24
1 inch 7 0.94 80.8 1.10 0.26
The composite oxide ore achieved excellent recoveries, >95% gold
extraction on crush sizes of � and � inch. At 1 inch crush size, the recovery
is about 81%.
Based on the agitation leach results, column leach tests using 4
inch x 4.56 feet cylinders were conducted to simulate the heap leach, on the
oxide ore at 1" and �" size
Table 2. Summary of cyanide column leach test results on the oxide
ore sample
Ore Type Crush Time Head % Au kg/T kg/T
(days) Extraction NaCN Ca(OH)2
Size g/t Au Usage Usage
Oxide 1 inch 24 0.94 93.1 0.42 1.01
1/2 inch 24 0.94 91.5 0.34 1.01
A high gold recovery of >91% was achieved on both columns in 24
days. Cyanide and lime consumption rates are normal for the composite oxide
sample. These results indicate that there should not be any complication to
recover gold from the oxide ore by heap leach. Further testing will be done on
>1 inch grind size.
Sulphide Ore:
Two flotation tests were conducted on a composite high grade
sulphide ore as shown in Table 3.
Table 3. Summary of flotation test results on the high grade
sulphide ore sample
Ore Type Grind Size Rougher Concentrate Total Rougher
Grades Recovery
g/t Au g/t Ag % Cu % Au % Ag % Cu
High Grade 80% -74um 3.40 24.16 0.46 99.3 99.2 96.5
Sulphide
80% -100um 2.75 23.56 0.45 98.5 99.1 98.2
80% -150um 2.39 24.01 0.45 97.9 98.2 96.3
*Note: "um" is micron
The Au, Ag and Cu recoveries are very high for all three grind
sizes from minus 74 to 150 microns (i.e. 0.074 to 0.15 millimetre), i.e. >97%.
Agitated cyanide leach test at finer grind sizes of 80% -86um on
the composite high-grade and low-grade sulphide ores were also conducted as
shown in Table 4.
Table 4. Summary of agitated cyanide test results on the sulphide
ore samples
Ore Type Grind Time Calculated % Au kg/T kg/T
Size (hrs) g/t Au Extraction NaCN Ca(OH)2
Usage Usage
High Grade 80% -86um 48 2.45 69 0.80 0.92
Sulphide
Low Grade 80& -86um 48 1.05 77 0.65 0.87
Sulphide
At minus 86 microns size (i.e. 0.086 millimetres), after 48 hours,
the high-grade and low-grade gold extraction was 69% and 77% respectively. The
leach time was then increased to 120 hours and using a finer grind size of
-50um the extraction was elevated to 81.4% and 79.7%.
Agitated cyanide leach tests on low-grade sulphide ore at 1, � and
� inch sizes recover about 63 to 65% after 7 days, indicating a slow leach
rate as well as high cyanide consumption (see Table 5)
Table 5. Summary of coarse cyanide test results on the low-grade
sulphide ore sample
Ore Type Crush Size Time Calculated % Au kg/T NaCN kg/T
(days) g/t Au Extraction Usage Ca(OH)2
Usage
Low Grade
Sulphide 1/4 inch 7 0.95 65.2 2.83 0.10
1/2 inch 7 0.94 66.0 2.88 0.15
1 inch 7 0.99 62.7 2.82 0.25
Column testing on the low-grade sulphide ore extracts about 40% of
the gold after 24 days with high cyanide consumption.
Table 6. Summary of cyanide column test results on the low-grade
sulphide ore sample
Ore Type Grind Size Time Head % Au kg/T NaCN kg/T
(days) Extraction Usage Ca(OH)2
g/t Au Usage
Low Grade 1/4 inch 24 0.99 39.0 0.98 1.01
Sulphide
Ball Bond Index:
A ball bond work index to test the hardness of the ore was also
completed. This test indicates the ore grinds at 23.9.kWh/tonne. This is a
hard ore and therefore a possible route for processing is to coarse grind the
ore, float the ore to get a cleaner concentrate and leach the concentrate
using cyanide.
Technical information in the Company news releases has been
reviewed and approved by Peter Tse who is the Manager and Senior Metallurgist
for PRA and has over 30 years of experience in the metallurgical field.
For Further Information:
Central China Goldfields plc Hanson Westhouse Limited
Dr. Jeffrey Malaihollo Anita Ghanekar / Martin Davison
Tel: 020 7621 0200 Tel: 020 7601 6100
Email: info@ccgoldfields.com
www.ccgoldfields.com
END
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