Compañía Minera Vizcachitas Holding (CMVH) and Sociedad Legal Minera San José Uno de Lo Vicuña, El y Piguchén de Putaendo (SLM San José), both wholly-owned subsidiaries of Los Andes Copper, hold favourable and valid title deeds to the mining concessions Vizcachitas mine project.
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Summary:
The Vizcachitas mineral deposit has similar characteristics to other Andean-style porphyry copper and molybdenum mineral deposits. This type of mineralized deposit contains large masses of hydrothermally altered rocks, sulphide-bearing small veins, disseminated sulphides, quartz veins and stockworks that may cover several square kilometres. These altered areas are commonly coincident with shallow intrusives, hydrothermal breccias and intrusion breccia.
The Vizcachitas Project is a complex set of porphyries and hydrothermal breccias intruded into a sequence of andesitic and daciandesitic volcanic rocks of the Abanico Formation of the EoceneOligocene age.
The activation of the magmatic chamber began with the injection of the precursor granodiorite. The barren inter-mineral granodiorite outcrops on the western margin of the system. The precursor granodiorite is a granodiorite biotite-hornblende porphyry, with age varying from 12.7 to 12.4 Ma. It is challenging to identify because it is texturally similar to the inter-mineral granodiorite, especially with the overprinting alteration.
The productive complex starts with a diorite with early porphyry character, compositionally fine to medium-grained quartz diorites dominate along with crowded dioritic porphyry segments. The diorites occur mainly north of the phreatomagmatic breccia body and on the western edge of the system. They may also extend north-west, but this area has not been adequately drilled.
A crowded porphyry is a porphyry or segments of a porphyry rich in phenocrysts with high granulometric contrast. They have a fine quartz-feldspathic fundamental mass, unlike other rocks of the intrusive complex, where the interstitial phases have a coarser grain size and their textures are more cohesive. A crowded porphyry is typically associated with magmas having a greater capacity to contain volatiles and, consequently, more likely to transport or contain a higher level of copper mineralization. The crowded porphyry is important in directing drilling programmes to target the most prospective areas of the Project. The early intrusive dioritic complex consisting mainly of quartz diorites but also including crowded porphyry segments is dated between 12.5 Ma and 12.58 Ma.
The next phases of intrusives are inter-mineral tonalitic and granodioritic phases. The age dating indicates little difference between these units, and they are probably from the same intrusive magma. The early inter-mineral tonalitic complex consists of crowded tonalites and dacitic porphyries and is dated between 11.8 and 12.08 Ma. The granodiorites, granodioritic porphyries and crowded granodioritic porphyries within the modelled area are part of the inter-mineral productive porphyries with an age of 11.9 Ma.
Mineral mapping using the Inductively Coupled Plasma-Mass Spectrometry assay data could not separate the two, also suggesting that they may be from the same intrusive complex (Halley 2018, Halley 2022). The earliest unit is of tonalitic character and crowded dacitic porphyries, which make up a sizable volume of rock of the Vizcachitas igneous complex. The late inter-mineral units of a granodioritic character are inequigranular granodiorites, granodioritic porphyries and crowded granodioritic porphyries. The tonalitic and granodioritic units are located on the southern edge and in a continuous corridor in the western part of the system.
Cutting through the volcanic and intrusive units are a set of hydrothermal and magmatichydrothermal breccias with a quartz-potassium feldspar-anhydrite matrix, local presence of biotite and associated chlorite. Two breccia bodies have been identified: the northern and southern breccias.
The final post-mineral phase of the intrusive complex is phreatomagmatic breccias or diatremes that intruded into the central part of the Project. Followed by a later set of dacitic composition dikes and plugs with preferential orientations north-south to NNE. The diatreme comprises polymictic breccias with a rock dust-clay-silica matrix or quartz-tourmaline matrix. Mineralized fragments are found at the margins of the diatreme breccia.
Mineralization
The latest mapping carried out by Los Andes Copper shows vertical zoning that is typical of porphyry-type systems. The first 10 m to 70 m thick upper zone is partially leached with some copper sulphides remaining, iron oxide mineralization, jarosite, goethite and, to a lesser extent, hematite. Copper oxides, such as chrysocolla, are occasionally observed in fractures.
Below the leached zone is a secondary enrichment zone or supergene zone of weak to moderate intensity, with chalcocite and covellite. The secondary minerals occur in fractures and as fine surface coatings on pyrite and chalcopyrite. The supergene thickness varies between 2 m and 100 m, with a mean thickness of 50 m, copper grades may exceed 1%, and the average grade for the supergene drilling is 0.47% Cu.
The hypogene or primary mineralization is mainly chalcopyrite, with pyrite. Bornite occurs in several of the drill holes below 800 m. In drill hole V2017-10, located in the northern area of the Project, bornite accounts for 15% of the total sulphides below 900 m, indicating that a possible bornite core could be found below the current drilling.
There is no correlation between the molybdenum mineralizing event and the copper mineralization. The molybdenite is associated with small B-type quartz veins and small late hydrothermal D-type veins.
Chalcographic studies conducted by GMC in 1998 and Los Andes Copper in 2020 show the local presence of grey copper sulphides (tennantite, tetrahedrite and enargite) in small amounts.
Veinlet Mapping 2020
During 2020 the consulting geologist Marco Carrasco carried out an 8 month programme to relog all the core, specifically to record the veinlet distribution and relationships with each other and with each intrusive phase. A total of 44,610 m of core were mapped from a total of 162 drill holes. During the 2021 to 2022 drilling campaign, the core was logged using the same veinlet classification scheme to ensure that all the data were compatible with the previous mapping.
Each lithological unit had a different distribution or morphology for the veinlets, probably due to the different chemical compositions and textures for each unit. For example, in andesites the Cveinlets are straight and thin and have little halo development.
Veinlets are estimated to control 70% of the copper mineralization and 90% of the molybdenum mineralization.
The veinlet interactions at different stages of the evolution of the hydrothermal system are:
• Lateral and vertical gradation: Compositional and morphological change laterally and vertically.
• Veinlet paragenesis: The intersection of the different vein types shows the temporal relationship between the different vein events.
• Hypogene enrichment: The mineralization of veins that are either barren or very weekly mineralized. For example, EDM-2 veinlets mineralized during the C-type veinlet event.
• Supergene enrichment: Exogenous processes that generate changes in the primary mineralogy of veins, for example, the coating of pyrite and chalcopyrite with chalcocite.
• Remobilization depletion: Pervasive hydrothermal solutions producing remobilization of pre-existing mineralization.
• Remobilization mutation: Compositional change of veins due to subsequent events, for example, biotites altered to chlorite. The total volume of veinlets in each metre was calculated by multiplying the number of veinlets per metre by their average width. The model was then generated from that value.
The following models were prepared:
• The sum of EDM-type + A-type + B-type + C-type – main copper veins
• C-type veins – the vein type which contributes the most copper to the system
• B-type – the main contributor of molybdenum to the mineralized system.