Ollachea Gold Project
Geology
The central area of potential economic interest at Ollachea is a 2 km long corridor in which local artisanal miners have been producing limited quantities of gold for some time from mineralized horizons that are exposed to surface. Minera IRL considers that a total of some 5 kilometres of strike is prospective for gold at Ollachea.
Intensely foliated and weakly convoluted, compact, metamorphosed, carbonaceous, black slate sedimentary packages of the Ordovician–aged Sandía Formation play host to the quartz veinlet-hosted auriferous Ollachea mineralization. Interstratified sub-parallel and tensional shearing is evident and clearly influences the continuity of gold-bearing veins and “mantos” (bedding-parallel suites of narrow quartz veins, veinlets and structures), imparting in places an intense foliation to the metamorphosed slate horizons. Low-angle east-west trending north-dipping faults play an important control on a local scale. Some minor sub-vertically oriented north-south horst-and-graben displacement of mineralized horizons is also recognized. Intra-bed faulting, sub-parallel to principal low angle faults is observed to control emplacement of the quartz-sulphide mineralization in quartz veining and shear zones; tight crenulation-like features probably represent an additional foci of mineralization.
Surface and underground geological mapping, geochemistry and surface ground magnetic results, together with diamond drilling logging data, confirm that mineralized veins and veinlets (generally 2-10 cm wide, but also occurring rarely up to 50cm thick) are controlled by the above-mentioned system of northerly dipping, east-west orientated thrust faults.
Alteration is mostly observed as extremely narrow borders or haloes to quartz veins/veinlets; and sometimes as minor alteration mineral inclusions within quartz. Low intensity silicification of the host slates is suggested where intense quartz vein/veinlet formation has occurred. Chlorite/ smectite are frequently observed, but not always. They occur as micro-veinlets within quartz veins/veinlets, narrow borders to mineralized structures and as replacement of pyrite, sporadically together with a possible very minor sericite component. Weakly disseminated pyrite-chlorite is sometimes observed along footwall or hanging wall contacts of mineralized structures.
Gold mineralization is found to be characterized by coarse to very fine free gold in erratic and discontinuous narrow quartz veinlets, in close association with primary sulphides pyrrhotite > arsenopyrite > chalcopyrite and a trace galena and sphalerite presence. Sulphides associated with quartz veinlets occur as semi-aligned disseminations (tiny specks, blebs and laminations) and at times as very narrow, crenulated micro-veinlets. A low gold tenor has been confirmed in areas interstitial to narrow mineralized veins and veinlets. A combination of lithology, structure, low intensity alteration/metamorphism and a presence of interstratified quartz veins/veinlets within layered shear zones have been interpreted as the principal combination of controls on gold mineralization at Ollachea.
Although no direct correlation is evident, there is an apparent association between gold mineralization and the presence of the magnetic mineral pyrrhotite. Processing of a 24 line-km geophysical ground magnetic survey has established 2 important east-west trending magnetically anomalous areas; coincident with best mineralized areas identified to date by exploration drilling from surface.
Ground Magnetic Anomalies
Drill Results
The results of drilling and resulting assay cross-sections are provided below under the heading “Assay Information” and “Cross Sections”.
True widths intersected range from approximately 60-94% of reported mineralized widths and average over 90% true width.
The following illustrates 2 typical transversal drill cross-sections for the Minapampa Zone and 1 for the Minapampa East Zone.
Underground Drilling
OLLACHEA PROJECT: 3-D CROSS-SECTION showing the topographic profile, a vertical & horizontal scale bar, the traces of existing drill stems (white), trace of the Challuno Exploration Access Tunnel (yellow), the Concurayoc and Minapampa Ore-bodies (red), and traces of programmed exploration extension drill holes (white)
Metallurgical
The results of Feasibility related metallurgical testwork demonstrate that gravity followed by conventional CIL treatment results in over 91% recovery of the gold at Ollachea.
Regional Exploration (Surrounding properties)
Regional geological exploration mapping and geochemical rock chip and stream sediment sampling has been completed over a total of 10,299 ha of concessions surrounding the Ollachea Project. Some 8,700 ha of concessions are retained by the Ollachea Project.
The regional geology comprises generally fine-grained prospective sedimentary sequences (gray slates, sometimes carbonaceous, and narrow, weakly developed intercalated siltstone/sandstone beds). Surrounding intrusive bodies include syenite (batholithic proportions), granodiorite and microdiorite.
Geological reconnaissance evaluation activities included the collection of some 242 regional stream sediment samples from the surrounding drainage system and 97 rock chip samples from potentially prospective outcrop. Several areas hosting prospective structures and occasionally quartz veins/ veinlets were sampled. All samples were analysed for gold by fire assay plus 36 ICP elements. Processed data identified three gold anomalous areas which are currently considered to be of lower exploration priority than the Ollachea 3 property.