Mirasol Reports Successful Initial Metallurgical Test Results on
High-Grade Vein/Breccia, Virginia Silver Project
VANCOUVER, Feb. 7, 2013 /CNW/ - Mirasol Resources Ltd.
(TSXV: MRZ), (Frankfurt: M8R) ("Mirasol") announces
initial results of a program of metallurgical test work at the
100%-owned Virginia Silver Project located in Santa Cruz Province, Argentina. The test program was designed
to determine how silver can be recovered from mineralized drill
core sourced from the Julia and Naty veins at the Virginia Project
(news release of June, 2012). Representative drill samples of the
high-grade vein and breccia-vein material were composited
separately from the surrounding halo of low-grade mineralization,
and were tested separately. Test results to a scoping level show
that the vein/breccia mineralization can be processed using
standard industry technologies with silver recoveries from 75% to
81%, through both agitated leaching and sequential
flotation/leaching methods.
Tests on the low-grade halo material, which
surrounds high-grade vein and vein/breccia, have not responded in
the same way, and to date have not resulted in potentially economic
recoveries. Mineralogical test work is underway to investigate the
host minerals for silver in the halo, with the goal to increase the
recoveries of the low-grade halo.
"Test work shows the high-grade vein/breccia,
the material which contains the majority of the silver present in
the Virginia silver vein system,
has good silver recoveries using proven, low risk
technologies. This is a major step forward for the Virginia
Project." said Mary Little,
Mirasol's President and CEO.
Technical Details
A master composite and individual composites of
vein/breccia material were prepared from samples taken from 34
representative drill holes from the Julia North, Julia Central, and
Naty veins. Fifty previously-assayed, individual intervals of
samples representing 53.1 metres of core with a total weight of
100.2 kilos, and were composed from sample reject material. In the
case of Julia North, an additional composite was made from 18
quarter-core samples representing 14.7 metres with a total weight
of 51.4 kilos.
Test work showed that the recoveries by both
standard flotation and leaching methods are grain-size dependent,
and moderately fine grinds are needed to ensure good silver
recoveries.
Optimized bottle-roll leaching tests on the
vein/breccia material averaged 75 - 80 % silver recovery using the
test conditions summarized in Table 1. While the primary grind was
moderately fine, the required residence time and reagent
consumption were modest by the standards of silver materials of
this type. Overall processing costs are likely to be quite modest
and the process provides a low technical risk.
Table 1. Leaching Tests -
Representative Summary |
Head
Grades
Silver
g/tonne |
Grain size
passing 80
microns
(µm) |
Concentration
NaCN g/L |
Reagent Consumption
(kg/t of cyanide feed) |
Silver Recovery
% |
NaCN |
CaO |
230 - 614 |
45 - 50 |
3 - 5 |
1.5 - 2.2 |
0.2 - 0.6 |
75 - 80 |
Flotation test work was carried out on the
sample reject material from Julia North, Julia Central, and Naty
Veins, and also on a sample of quarter-core material from
Julia North Vein, in order to assure
that reject material was not more oxidized than core, which could
potentially affect silver recoveries. Results showed that the
responses from samples made from core and reject material do not
differ at Julia North. Visually, the core is highly oxidized, but
mineralogical studies have shown that the main silver mineral is
acanthite, a silver sulphide (87% silver). Flotation tests were
moderately successful in concentrating acanthite into rougher
concentrate with recoveries of 66 to 71 % (Table 2). Subsequent
regrinding and intensive leaching of the rougher concentrates
recovered greater than 98% of the silver in the concentrates,
indicating that silver dore could be made from the concentrates
with very small losses, producing a high value product (Table
2).
Table 2. Flotation Tests -
Representative Summary |
Head
Grades
Silver
g/tonne |
Grain size
passing 80
microns
(µm) |
Rougher Con 1-
4 Grade
Ag g/t |
Mass Pull
% |
Tail
Ag g/t |
Silver Recovery % |
315 - 421 |
49 - 84 |
2,630 - 6,300 |
4.4 - 10.4 |
124 148 |
66 - 71 |
Note - intensive CN
leaching of float concentrate resulted in > 98% recovery of
contained silver |
Furthermore, leaching of the flotation tails was
successful in recovering additional silver. The tests done to date
produced combined flotation/leaching recoveries of 79 - 81% of the
silver (Table 3).
Table 3. Combined Flotation and
CN Leach of Tails Tests - Representative Summary |
Head Grades
Silver g/tonne |
Regrind Grain
size passing 80
microns (µm) |
Flotation Silver
Recovery % |
Additional CN
Leaching Silver
Recovery % |
Combined Silver
Recovery
% |
315 - 421 |
40 - 45 |
71.2 |
7 - 10 |
79 - 81 |
In summary, the vein/breccia samples have shown
they respond well, and produced silver recoveries in the range of
75% - 81%, using technologies that are proven worldwide and in use
at the three precious metal mills operating in the province of
Santa Cruz (Cerro Vanguardia, San
Jose and Manantial Espejo mines).
Metallurgical recoveries on the halo composite
of low-grade mineralization surrounding the Julia North, Central,
South, and Naty veins do not achieve those of the vein/breccia
material. Mineralogical studies combined with the
metallurgical test results to date suggest that the halo contains
some acanthite which is being recovered, but that the majority of
the silver in the halo is present in other minerals. The next phase
of work on the halo sample will be mineralogical in order to better
understand the silver mineralogy.
Chris Martin, C.
Eng; Principal Metallurgist with Blue Coast Metallurgy Ltd., is the
Qualified Person that has supervised the metallurgical test work
conducted primarily at Blue Coast Research Ltd. in Parksville, British Columbia, Canada, and has
read and approved the technical content of this news release.
Paul G. Lhotka, Principal Geologist
for Mirasol, is the Qualified Person under NI 43-101 who has
approved the technical content of this news release for
Mirasol.
Quality Assurance/Quality Control:
Exploration at Mirasol's Projects is supervised by Stephen C. Nano, Vice President of Exploration;
Timothy Heenan, Exploration Manager;
and Paul Lhotka, Principal Geologist
who is the Qualified Person under NI 43-101. All technical
information for the Company's projects is obtained and reported
under a formal quality assurance and quality control (QA/QC)
program. Drill core, rock chip and stream sediment samples are
collected under the supervision of Company geologists in accordance
with standard industry practice. Samples are dispatched via
commercial transport to an ISO 9001:2000-accredited laboratory in
Mendoza, Argentina for analysis.
Results are routinely examined by an independent geochemist to
ensure laboratory performance meets required standards.
Assay results from diamond drill core or RC
drill samples may be higher, lower or similar to results obtained
from surface samples.
Neither the TSX Venture Exchange nor its
Regulation Services Provider (as that term is defined in the
policies of the TSX Venture Exchange) accepts responsibility for
the adequacy or accuracy of this release.
SOURCE Mirasol Resources Ltd.