Metallurgy

Metallurgical Testwork

Metallurgical testing is on-going to assess the most commercially beneficial method to produce silver/copper concentrates from the high-grade Strieborná deposit for sale to custom smelters.

Test work will be used to design the process facilities to be included in a Preliminary Economic Assessment. Three basic process alternatives are being considered. Each starts with simple flotation concentration to recover the primary silver/copper bearing minerals. Downstream processing of these concentrates will likely include roasting or selective flotation of the concentrates to safely eliminate mercury (Hg) prior to shipment to the smelter. A third process alternative includes the leaching of the concentrates to recover contained antimony (Sb) and produce it as a marketable co-product.

Blue Coast Metallurgy Ltd, the Company’s principal metallurgical consultant, has recommended a series of follow-up investigations planned to yield sufficient criteria for initial engineering design. These tests are now under way.

Flotation Concentration

Initial testing indicates the best overall grade recovery curve resulted in a silver/copper concentrate assaying approximately 5800g/t Ag and 25% Cu at a 94% silver recovery and a 96% copper recovery. Concentration consisted of a rougher circuit and single stage cleaner flotation upgrade. This indicates that simple two-stage flotation, a common process, will likely be used to make silver/copper concentrates.

Antimony Recovery

Recovering antimony from the concentrate prior to shipment to a custom smelter has two potential benefits. The antimony recovered from the concentrate to a solution can be used to form various marketable antimony products for sale as by-products. Secondly, the residual concentrate containing silver and copper can be sent to a smelter with no or little penalty for antimony content. The potential for antimony removal from the concentrates by leaching in caustic solution at varying reagent concentrations and temperatures was evaluated.

The following table summarizes the leaching results:

Concentrate Leaching Results
Test No.	Temp °C	Sb in Residue (%)	Recovery to solution(%)
Head Sample Sb Content 18.1%
Test 1	95	0.5	97
Test 2	95	4.9	73
Test 3	95	1.0	95
Test 4	85	2.0	89
Test 5	95	3.7	80

The leaching tests also measured mercury and arsenic recovery from the concentrates to the solutions. Mercury extraction varied from 67% to 92% while arsenic recovery varied from 6% to 19%.

Although further testing has demonstrated that leaching of antimony as a by-product is technically feasible the Company has decided to postpone a decision on its implementation until after the start of initital silver/copper production. This will eliminate a significant development capital expense.

Mercury Removal

The level of mercury in Strieborná concentrates, without removal prior to shipment, renders the concentrate unacceptable at custom copper smelters. Hence, ways to reduce the mercury (and antimony) contents prior to shipping the material to a copper smelter are required. The preliminary results indicate that roasting of concentrates prior to shipment can lead to a marketable concentrate with virtually all mercury eliminated.

A number of experimental tests were conducted to examine mercury (and antimony) removal from Strieborná copper concentrate by first roasting the concentrate in an inert or neutral gaseous atmosphere to volatilize mercury (thus avoiding the oxidation of sulphur to sulphur dioxide), followed by an oxidizing roast to volatilize antimony oxides and some sulphur.

Antimony elimination was more problematic although marketing studies indicate that smelters would accept these concentrates (with an appropriate penalty).

The tests were designed and supervised by pyrometallurgical specialists associated with Blue Coast Metallurgy Ltd.

Results for the suite of roasting tests are summarized in the tables below:

Results for Laboratory Hg Volatilization Tests on Strieborna Concentrate
Test No.	Conditions	Starting material and initial weight of sample, gm	Cu %	Fe %	S %	Sb %	Hg (ppm)
	Head Sample		22.6	15.2	22.4	17.7	7210
1	600° C N₂ Atmosphere	Green Conc. 15 gm	25.5	16.5	23.2	18.9	2170
2	750° C N₂ Atmosphere	Green Conc. 15 gm	27.3	18.8	24.0	18.3	0.5
3	950° C N₂ Atmosphere	Green Conc. 30 gm	29.3	20.5	23.6	15.1	10.9
4	950° C Air Atmosphere	Test 3 Calcine 15 gm	30.5	21.2	1.18	15.2	<0.3

Calculated Elimination of Hg, Sb and S in Roasting Tests
		% Elimination in Each Test
Test No.	Condition	Hg	Sb	S
1	600° C N₂	69.9	0.4	2.6
2	750° C N₂	99.9	11.0	7.8
3	950° C N₂	99.9	33.6	17.5
4	950° C Air	99.9	35.7	95.2

Further testing to provide design parameters for an economic assessment is now on-going under the supervision of Blue Coast Metallurgy. Roasting options (together with environmentally safe recovery of the mercury for sale or other disposal) are being considered and will be evaluated as part of a Preliminary Economic Assessment the Company is preparing.

The Company is also investigating the use of selective flotation to evaluate the possibility of removing mercury bearing minerals from the concentrate which could, if successful, eliminate the need for concentrate roasting.