Colombia Goldfields Reports Successful Metallurgy Test
Fri Apr 18, 8:31 AM
ca.news.finance.yahoo.com
TORONTO, April 18 /CNW/ - Colombia Goldfields Ltd. (the "Company") (TSX: GOL/OTCBB: CGDF) ("CGL" or the "Company") announced today that it has received the results of independent testing of the metallurgical properties, including projected recoveries, of samples from the Company's Marmato Mountain Gold Development Project in Colombia.
Recovery rates of up to 92% were achieved depending upon the chosen flowsheet. SGS Lakefield Research conducted the test on two composite samples, each containing material representative of the ore grades at Marmato.
"These results confirm our view that very high recovery rates using conventional technology are likely to be achieved when Marmato is put into production," said J. Randy Martin, Vice Chairman and CEO, Colombia Goldfields Ltd. "They also are consistent with recoveries from existing production at the mill located on Zona Baja (Lower Zone) at Marmato, where recoveries of more than 88% are being achieved using gravity separation followed by flotation, then leaching of the flotation concentrates."
Colombia Goldfields recently won the bidding process to acquire the Zona Baja (see press release January 30, 2008) from Mineros Nacionales S.A. (Mineros) Mineros operates an underground mine on the Zona Baja that feeds ore to a mill using conventional grinding technology. Production is approximately 25,000 ounces of gold per year.
Highlights of the report include:
- The following methodologies were all shown to be viable:
- Gravity separation followed by the flotation of the gravity tails
and cyanidation of the flotation concentrates;
- Gravity separation followed by cyanidation of the gravity tails;
- Heap leaching
- Gravity separation followed by cyanidation of the gravity tails
resulted in the highest recoveries of 92%
Detailed Findings
Gravity Separation
------------------
A concentrate sample that was tested produced the following results:
Summary of Gravity Separation Tests
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Test No. K(80) Gravity Concentrate Grav Tail Head (calc)
um Wt% Au, g/t %Au Rec,y Au, g/t Au, g/t
-------------------------------------------------------------------------
G1 89 0.027 1819 39.0 0.77 1.26
-------------------------------------------------------------------------
G2 96 0.071 375 25.6 0.77 1.10
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The sample contained significant free gold with 25.6 to 39.0% of the total
gold being recovered by gravity separation. This finding is consistent with
the experience of artisinal miners at Marmato Mountain who use gravity
separation to recover gold.
Cyanidation of the Gravity Tails
--------------------------------
Overall gold recoveries from ore that was gravity separated and exposed to
cyanide was in the 89 to 92% range, depending on the fineness of grind. This
testwork revealed that gold extraction rose by approximately 10% when ore
concentrates were reground to a K(80) of 64 microns. Results are summarized
below:
Summary of Cyanidation Tests
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Test K(80) Reag. Cons Au Res. CN % Au Recovery Head Au, g/t
No. kg/t Ext'n Au Feed Over-
% g/t Au all
um NaCN CaO 24h g/t Gray CIL Comb Calc. direct
-------------------------------------------------------------------------
CIL1 64 0.75 2.36 86.4 0.11 0.77 39.0 52.7 91.7 1.26 1.19
-------------------------------------------------------------------------
CIL2 89 0.82 2.63 81.6 0.14 0.76 39.0 49.8 88.8 1.26 1.19
-------------------------------------------------------------------------
The extraction of gold was 81.6% without regrinding and 86.4% after
regrinding to a K(80) of 64 microns. This resulted in overall gold recoveries
by gravity separation and CIL of 88.8% at a K(80) of 89 microns and 91.7% at a
K(80) of 64 microns.
Flotation
---------
Flotation testwork was done in two stages. Initially two rougher flotation
tests were performed to investigate the effect of fineness of grind on the
recovery of gold in a bulk rougher concentrate. Subsequently two "cleaner"
flotation tests were performed to investigate upgrading the rougher
concentrate. Recoveries were generally high; in one sample recovery was 95.5%
in 7% of the weight of the test.
Cyanidation of flotation tails
------------------------------
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Test K(80) Reag. Cons. Reag. Cons. % Resi- CN % Au Recovery
No. um kg/t of CIL kg/t of ore Extr'n due Feed Overall
feed NaCN CaO Au Au Au Grav Flot CIL Comb
NaCN CaO 48h g/t g/t
-------------------------------------------------------------------------
Feed: F3 Ro Conc
-------------------------------------------------------------------------
CIL3 45 2.76 4.22 0.46 0.70 78.0 0.91 4.14 25.6 70.4 54.9 80.5
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CIL4 25 2.99 3.32 0.49 0.55 88.5 0.54 4.70 25.6 70.4 62.3 87.9
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Feed: F5 Cl Conc
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CN5 87 4.58 3.83 0.32 0.26 74.1 4.26 16.4 0 95.5 70.8 70.8
-------------------------------------------------------------------------
CN6 21 3.15 2.54 0.22 0.18 81.4 3.37 18.1 0 95.5 77.7 77.7
-------------------------------------------------------------------------
The best results were achieved in test CIL-4, which showed 88.5% gold
extraction and an overall gold recovery of 87.9% by gravity separation,
flotation and concentrate cyanidation.
Heap Leaching - Bottle roll testing of various crush sizes were conducted
during this testwork. The results are summarized below:
Summary of Heap Leach Amenability Tests
-------------------------------------------------------------------------
Test Feed Crush Size Reag. Cons. Au Residue Head Au, g/t
No. Kg/t Extr'n Au
%
NaCN CaO 24h g/t calc. direct
-------------------------------------------------------------------------
CN2 Comp1 Minus 1/4 in 0.58 2.51 85.7 0.06 0.38 0.29
-------------------------------------------------------------------------
CN3 MET-05 Minus 1/2 in 1.51 4.25 84.3 0.21 1.31 1.19
-------------------------------------------------------------------------
CN1 Comp1 Minus 3/4 in 0.62 2.37 77.7 0.07 0.29 0.29
-------------------------------------------------------------------------
CN4 MET-05 Minus 1 in 1.46 6.91 73.6 0.35 1.33 1.19
-------------------------------------------------------------------------
These heap leach results indicate that the samples were amenable to heap
leaching at the finer crush sizes, half inch and quarter inch, in which gold
recoveries were 84.3% and 85.7% respectively.
Other Properties - The testwork denoted additional metallurgical
properties of:
- Bulk density of 2.61 (g/cm(3))
- Abrasion index of 0.58 (standard bond procedure)
- Indicating fairly abrasive ore
- The bond work index of 15.0 (metric) with a P(80) of 114 microns
- Indicating moderate hardness
Summary of Overall Results
--------------------------
The overall results for the various flowsheets appears below:
-------------------------------------------------------------------------
Flowsheet O'all Au Overall Tail Head O'all
Recovery Au, g/t (calc) NaCN
% Au, g/t Cons.
kg/t
of ore
-------------------------------------------------------------------------
Heap Leach 84 0.21 1.31 1.5
-------------------------------------------------------------------------
Gravity - CN 89-92 0.11-0.14 1.26 0.8
-------------------------------------------------------------------------
Gravity - Ro Flot - Conc CIL 88 0.13 1.04 0.5
-------------------------------------------------------------------------
CI Flot - Con CN 78 0.36 1.50 0.2
-------------------------------------------------------------------------
Further Steps
-------------
Based on the results from the test program, SGS Lakefield has made the
following recommendations for further metallurgical testwork:
- Conduct column heap leach tests to determine the effect of leach time
on the recovery of gold, the need for agglomeration and confirm the
effect of particle size;
- Optimize the flotation conditions;
- Optimize the leach conditions for cyanidation of the flotation
concentrate, including fineness of grind, cyanide concentration, lead
nitrate addition, and carbon addition;
- Conduct a cyanide balance to determine the major cyanide consumers
and optimize the conditions to minimize reagent consumption;
- Investigate cyanide destruction and possibly cyanide recovery
methods;
- Conduct thickening tests on the flotation concentrate;
- Conduct grinding tests to design the grinding circuit
- Conduct a variability program once the optimum processing conditions
are established.
About Colombia Goldfields
Colombia Goldfields Ltd., through its subsidiaries Compania Minera de Caldas S.A. and Gavilan Minerals S.A., is developing what it believes is a multi-million ounce gold resource in Colombia's historic Marmato Mountain gold district.
Colombia Goldfields is traded in the US under the symbol CGDF, on the Toronto Stock Exchange under the symbol GOL, and in Germany under the symbol C2B.
Disclaimer
This release contains forward-looking statements that are based on the beliefs of Colombia Goldfield's management and reflect Colombia Goldfield's current expectations as contemplated under section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities and Exchange Act of 1934, as amended. When used in this release, the words "estimate, "project," "believe," "anticipate," "intend," "expect," "plan," "predict," "may," "should," "will," "can," the negative of these words, or such other variations thereon, or comparable terminology, are all intended to identify forward-looking statements. Such statements reflect the current views of Colombia Goldfields with respect to future events based on currently available information and are subject to numerous assumptions, risks and uncertainties, including, but not limited to, risks and uncertainties pertaining to development of mining properties, changes in economic conditions and other risks, uncertainties and factors, which may cause the actual results, performance, or achievement expressed or implied by such forward-looking statements to differ materially from the forward looking statements. In particular, there is no assurance that a definitive agreement will be executed or that the proposed transaction will be completed.
Contacts
Company Contact: J. Randall Martin
Vice Chairman and CEO
Colombia Goldfields Ltd. (TSX: GOL/OTC BB: CGDF)
8 King Street East
Suite 208
Toronto
Ontario
M5C 1B5
T: (416) 361-9640
F: (416) 361-0883
info@colombiagoldfields.com
www.colombiagoldfields.com
U.S. Investor Relations: John Menditto
Roth Investor Relations
Inc.
Tel. (732) 792-2200
Email: johnmenditto@rothir.com
Canadian Investor Relations: Martti Kangas
Colombia Goldfields
Ltd.
Tel: (416) 361-9640
martti@colombiagoldfields.com |
