Sep 17 2013
Solvista Gold Corporation is pleased to announce the recommencement of drilling at its Caramanta Project, designed to test the Malabrigo and Casa Verde porphyry targets, located to the immediate north of the three targets already drilled by with Company within the Caramanta Porphyry Cluster ("CPC"). The Company is also pleased to announce the results of encouraging first pass metallurgical studies and associated petrographic analyses on the El Retén porphyry system.
Highlights
- Drilling will commence on the Malabrigo porphyry target, which is located 500 metres to the northwest of Ajiaco Sur, as shown on Figure 1. Exploration at Malabrigo has defined a roughly north-south trending 75th percentile gold anomaly (0.18 g/t) measuring approximately 650 metres by 250 metres. Surface channel samples have returned values up to 1.20 g/t Au and 0.17 % Cu.
- Drilling will also test the Casa Verde porphyry target, located 600 metres to the north-northeast of Malabrigo. Exploration at Casa Verde has defined a roughly north-south trending 75th percentile copper anomaly (731 ppm) measuring approximately 700 metres by 140 metres. Surface channel samples have returned values up to 0.94 g/t Au and 0.45 % Cu.
- Petrographic and SEM analyses conducted on selected samples from the El Retén porphyry system confirmed the presence of gold in three distinct compositional groups with a clear spatial association to copper, mostly as chalcopyrite and minor bornite.
- First pass metallurgical (flotation) test work conducted on a composite sample of material from the El Retén drilling program resulted in encouraging recoveries.
- The El Retén, El Corral and Ajiaco Sur targets of the Caramanta Project are located within a regional environmental designation known as a "District of Integrated Management" or "DMI", which in 2011 created a prohibition on open pit mining activity. The Company completed its Phase 1 drill program in March 2013, pursuant to the requirements of the DMI designation and has no plan to resume exploration on these targets until the completion of its Phase 2 drilling program at the Malabrigo and Casa Verde targets, which are located outside the DMI, in 2014 and resolution of the ongoing DMI removal application. The Company has requested the removal of the DMI designation in the area of the mining concession to facilitate any future mining activities. The Company has been advised that no further exploration may be conducted within the DMI until the application to remove the DMI designation has been considered.
Commenting on the developments, Solvista's President and CEO, Miller O'Prey, stated "We are very pleased to be starting drilling again at our Caramanta Project and to be testing two more of the targets we have defined as we strive to define the potential size of the CPC, just one of a number of promising targets we have on the property. Likewise we are pleased to announce initial positive metallurgical studies as part of our work program to further de-risk the Project."
Preliminary Petrographic Studies of El Retén Mineralization
Four drill core samples of representative mineralization from the El Retén Au-Cu porphyry were sent to GeoMinEx in Canada for polished thin section preparation and petrographic examination of the nature of alteration and mineralization. After the petrographic studies were completed, the four samples were studied with a scanning electron microscope to further assess and document the gold and copper mineralization.
The thin section petrography confirms what Solvista Gold geologists have observed in surface outcrops and drill core. The gold-copper mineralization at El Retén is dominantly associated with veins and fractures related to the early potassic and later actinolite-magnetite alteration. The veins comprise variable amounts of quartz ± magnetite ± actinolite ± potassium feldspar. Biotite, carbonate, epidote and tourmaline are minor vein constituents. Albite, suspected to be present previously by SVV geologists, was identified in some vein envelopes indicating that at least some of the actinolite-magnetite alteration can properly be called sodic-calcic alteration, an important alteration type in IOCG and other porphyry Au-Cu deposits. Disseminated mineralization does not appear to be volumetrically important at this time.
Gold occurs in three distinct compositional groups - electrum with 84% Au and 16% Ag, electrum with 68% Au and 32% Ag and native Au (100% Au). Copper occurs as predominantly as chalcopyrite and less commonly as intergrowths with bornite. The Au-Cu mineralization is accompanied by trace amounts of sphalerite, galena, pyrite and rare acanthite (Ag2S). The chalcopyrite-dominant nature of the copper mineralization suggests that the magmatic-hydrothermal system as defined by the limits of the current drilling may be in the outer portion of the potassic core of the system and that the typically higher grade, bornite-rich portion of the potassic alteration zone has not been drilled.
The electrum and native gold occur along silicate-silicate, silicate-sulphide or silicate-sulphide-magnetite contacts. Several examples of electrum apparently encapsulated in chalcopyrite were observed; however, electrum/native gold was not found encapsulated in silicates (important with respect to gold recovery by flotation methods). The occurrence of gold in three distinct compositional groups is strong evidence that the Au-Cu mineralization at El Retén is the result of a dynamic, polyphased magmatic-hydrothermal system as the Company has suggested in previous press releases. Figure 2 is a reflected light photomicrograph of a sample from drill hole CAD-1218 at 398.98m showing gold, as electrum, located along the interface between a compound sulphide aggregate (chalcopyrite and bornite) and silicates.
Preliminary Flotation Test Work on El Retén Mineralization
A composite sample of approximately 40 kilograms of crushed drill core (coarse rejects) was prepared from equal amounts of altered and mineralized porphyry and volcanic rocks, the primary host rocks for the Au-Cu mineralization at El Retén. The 40 kilogram composite sample was homogenized and split into equal halves, with one half being sent to Global Mineral Research Limited ("GMR") in Vancouver for first pass rougher flotation test work. The sample was split into representative test samples and a head grade assay (original and duplicate) at GMR yielded average values of 0.99 g/t Au, 0.20% Cu and 0.53% total sulfur, in good agreement with the original composite analyses completed by Solvista (1.07 g/t Au, 0.19% Cu and 0.55 % S).
A 2 kilogram sample was then ground to 80% passing 77 microns and was used for the 3-stage rougher flotation test work. Typical reagents (SIPX, 3418A and MIBC) were used and the test yielded recoveries of 73% and 85% and concentrate grades of 12.94 g/t and 2.78% for Au and Cu, respectively, at a natural pH range of 8.3-8.9. The mass yield of the concentrate was only 5.9%.
Discussion of the Test Work Results
GMR described the results as "very promising" and noted that the sample was received as previously crushed rock that may have been partially oxidized which could have adversely affected the recoveries. Furthermore they state that "the material appears to be amenable to the flotation process as good copper and gold recoveries are achieved in a very low mass yield. Further optimization tests are recommended to optimize the flotation procedure, and cleaning of the rougher concentrate should be investigated to determine if a saleable grade product may be produced. Coarser primary grinds may achieve similar results which can potentially reduce operating costs."
The results are viewed by the Company as being sufficiently encouraging to warrant a more extensive metallurgical test program including magnetic separation, leaching, optimization of grind size and variations in the reagents used on a more representative sample suite.
Source: http://www.solvistagold.com/