Malbex Resources Inc. (TSX VENTURE:MBG) announced results today from preliminary metallurgical testing of samples from the Company's Del Carmen Norte gold-silver project in San Juan province, Argentina.
Overall, test results indicate good potential for heap leach cyanidation treatment and for whole ore milling/cyanidation treatment of the materials represented by the five composite samples tested. Most encouraging are results from material crushed to 6.3 millimetres (mm) to obtain preliminary information on heap leach amenability. Four of five 6.3 mm samples had Au recoveries ranging from 78.3 to 83.1% while the fifth sample showed 61.4% recovery, with an overall average of 76.5%. Silver recoveries ranged from 15% to 65% for those samples with detectable silver (four of five) and were generally higher for milled compared to crushed material. Cyanide consumption for all samples was low with an average for all tests of 0.16 kg/t.
"We're very encouraged by the results of initial metallurgical testing, which confirm our earlier observations that the Au-Ag mineralisation at Del Carmen Norte is strongly oxidized and amenable to extraction of gold by low-cost heap leach technology," said Tim Warman, President & CEO. "Our next goal is to complete sufficient drilling to demonstrate continuity of mineralisation in the Rojo Grande area, and support an initial resource calculation. We have also commenced the first drill test of a large resistivity target at Cerro Amarillo, identified by last season's geophysical surveying."
The metallurgical samples are roughly 15 kilogram (kg) composites of previously sampled half core (i.e., quarter core) that are representative of the average grades of significant intervals of mineralisation at the Rojo Grande (samples RG1, RG2 and RG3) and Naciente Quebrada Pedregosa (samples NQP1 and NQP2) targets at Del Carmen Norte. Average measured head grades for the composites range from 0.67 to 2.21 grams per tonne (g/t) Au compared to a range of 0.57 to 2.64 g/t Au in the selected intervals.
Compositing and metallurgical testing was carried out by McClelland Laboratories Inc. of Sparks, Nevada. Each composite was crushed to determine gold and silver recoveries at four feed sizes based on 80% passing (P80) 12.5 mm, 6.3 mm, 212 micron (µm) and 150 µm. The testing provides information on sensitivity of cyanidation to feed size, recovery rates, reagent requirements, and variability of potential ore at Del Carmen Norte. The crushed feeds (12.5 mm and 6.3 mm) provide preliminary information on the amenability to heap leaching. The milled feeds (212 µm and 150 µm) test the amenability of each composite to milling and agitation cyanidation treatments such as carbon-in-pulp (CIP).
Direct leaching (bottle roll) tests indicate the mineralisation intersected in previous drilling represented by five composite samples from the Rojo Grande and Naciente Quebrada Pedregosa targets at the Del Carmen Norte prospect are amenable to cyanidation processing of either crushed or milled material. Gold recoveries for each milled fraction (212 µm and 150 µm) ranged from 82% to 89% after 72 hours of leaching with comparable results for both size fractions. Gold recoveries after 96 hours of agitation were lower for crushed material compared to milled fractions and were clearly improved by the reduction from 12.5 mm to 6.3 mm. Four of five 6.3 mm samples had Au recoveries ranging from 78.3 to 83.1% while the fifth sample showed 61.4% recovery.
The Del Carmen Norte prospect consists of the roughly 3 by 3 kilometre (km) high-sulphidation hydrothermal system consisting of silicification, quartz-alunite, advanced argillic (kaolinite) and argillic (illite) alteration. Rojo Grande consists of prominent reddish weathering silicified outcrops on the northern flank of the massif of high sulphidation hydrothermal alteration. Clay (argillic and advanced argillic) and quartz-alunite alteration and silicification typically lighten the normally darker, intermediate volcanic rocks affected by the hydrothermal alteration. Diamond drilling has intersected near-surface Au-Ag mineralization at Rojo Grande over an area about 200 m by 150 m including intervals of:
- DDHC-10-017: 41 m grading 1.18 g/t Au and 31.2 g/t Ag (1.70 g/t Au-EQ)
- DDHC-10-018: 15 m grading 1.07 g/t Au and 27.3 g/t Ag (1.53 g/t Au-EQ)
- DDHC-10-020: 124.5 m grading 0.57 g/t gold (Au) and 8.8 g/t silver (Ag) (0.72 g/t Au-EQ)
- DDHC-10-031: 38 m grading 0.88 g/t Au and 12.2 g/t Ag (1.09 g/t Au-EQ)
- DDHC-10-032: 142.15 m grading 0.88 g/t Au and 13.7 g/t Ag (1.11 g/t Au-EQ), including 40.15 m grading 1.45 g/t Au and 19.6 g/t Ag (1.78 g/t Au-EQ)
- DDHC-10-034: 73 m grading 0.74 g/t Au and 17.4 g/t Ag (1.03 g/t Au-EQ)
Although fresh sulphides, mainly pyrite, occur in flanking, mainly barren clay-altered rocks, intervals of silicification and quartz-alunite alteration which host virtually all of the Au-Ag mineralisation lack visible sulphide minerals. Mineralization at Rojo Grande is hosted by vuggy silica and massive silicification with fine-grained hematite, goethite and jarosite veinlets and red-brown staining. The silicified outcrops at Rojo Grande are interpreted to be part of a sub-horizontal sheet formed by preferential silicification and quartz-alunite alteration of volcanic breccias within the altered volcanic sequence. Northeast-striking zones of hydrothermal breccias cemented by chalcedony and very fine-grained quartz locally cut pre-existing silicification. Many of the above intersections are bounded by changes in style of alteration, faults or both as altered rocks are cut by northeast-, north-northwest- and east-striking fault zones. While some faults clearly post-date the hydrothermal events (they displace and truncate silicification for example), hydrothermal feeder structures that controlled alteration and mineralization are inferred to preferentially coincide with one or more fault directions.
The Naciente Quebrada Pedregosa prospect lies within predominantly quartz-alunite alteration about 1,200 m south of the Rojo Grande target where mapping identified northeast-striking silicified structures with up to 165 g/t Au in surface samples (see PR of February 17, 2010). DDHC-10-023 contained the best results in the four-hole fan drilled to test this difficult to access target with multiple intercepts of mineralization apparently hosted by altered structures cutting dacitic volcanic rocks within the primarily andesitic sequence that includes:
- DDHC-10-023: 49 m grading 1.11 g/t Au, 21 m grading 1.69 g/t Au and 16 m grading 2.64 g/t Au and 6.08 g/t Ag
The metallurgical samples at Naciente Quebrada Pedregosa were composited from the longest zone of mineralization (NQP1) and the lowermost, slightly less silver-deficient mineralization (NQP2) in hole DDHC-10-023. The metallurgical samples at Rojo Grande were composited from the two longest intervals of Au-Ag mineralisation in holes DDHC-10-020 (RG1: entire 5.5-130m interval) and DDHC-10-032 (RG2: near-surface 34 m interval (23-57m); RG3: lowermost 40 m (124-164m)).
The 147 km2 Del Carmen concession package is located near the southern end of the El Indio Gold Belt, and hosts the Del Carmen Norte and Del Carmen Sur high sulphidation epithermal gold-silver systems. The Del Carmen Norte hydrothermal alteration covers approximately 9 km2. A second, less exposed, high sulphidation epithermal system occurs at Del Carmen Sur some 5 km to the south of Del Carmen Norte.
Del Carmen Norte consists of a strongly altered, sub-horizontal sequence of andesitic volcanic rocks that is cut by numerous faults. Volcanic breccias appear to be selectively silicified with silicification hosting mineralization sandwiched between less favourable argillic altered volcanic layers. Steep faults have strongly influenced hydrothermal fluid flow within the volcanic sequence. High-sulphidation alteration is therefore zoned outward from the combination of both lithological and structural controls on silicification. Controlled source audio-magneto-telluric surveying (CSAMT) in the previous field campaign identified elevated resistivity coincident with silicified rocks at Rojo Grande. Other larger CSAMT resistivity anomalies to the southwest are directly associated with steam-heated siliceous alteration at high elevations at Cerro Amarillo but continue to the depth limits of detection of the survey (roughly 500 m vertical).
In addition to Rojo Grande, other zones of vuggy silica and other styles of silicification, and enargite-bearing quartz veins on surface were drill tested in the 2009-2010 field campaign. The current 10,000 m drill campaign will focus on defining the extent of Au-Ag mineralization at Rojo Grande, testing the large CSAMT resistivity anomalies, and follow up on previous encouraging results from Naciente Quebrada Pedregosa.
Technical Information
Diamond drill hole samples consist of HQ-3 (6.11 cm diameter) core that is sawn in half by electric saw on site. Core samples are sealed in new plastic bags, which are inserted into rice sacks for transport by Malbex personal or commercial trucking service to ALS Global prep lab in Mendoza. All samples are crushed and pulped and powders sent by ALS to one of their laboratories (typically La Serena, Chile or North Vancouver, BC). Fire assay for gold is conducted on 30 gram (g) pulps with atomic absorption finish. Over limits (>10 g/t Au) are fire assayed with gravimetric finish. In addition, all samples receive multi-element analysis including silver by ICP after aqua regia digestion and mercury by cold vapour atomic absorption.
Malbex's quality assurance-quality control (QA-QC) program consists of the insertion in every 20 samples of at least one certified standard of known gold content, one blank (sample known to consist of very low levels of gold to ensure adequate cleaning of the sample preparation equipment between samples) and one field duplicate. Samples of significant drill intercepts will be sent to two additional independent laboratories to verify gold and silver analyses when necessary. Metallic screen fire analyses for gold will also be run regularly on discovered mineralization as an additional QA-QC check. The half core remaining after sampling is stored in a Malbex-run facility in San Juan for verification and reference purposes.
Peter Stewart, PhD, Vice-President Exploration of Malbex Resources Inc., is a Professional Geoscientist in the Province of Ontario, and is the Qualified Person as defined by NI 43-101 responsible for the technical information presented in this news release.
Source: Malbex Resources Inc.