On June 28, 2024, Aris Mining Corporation closed the acquisition of an additional 31% interest in the Soto Norte gold-copper project, increasing its total ownership in the joint venture to 51%. Mubadala Investment Company is retaining a 49% interest in Soto Norte gold-copper project.
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Summary:
The Soto Norte mineral deposit is classified as a high-sulphidation epithermal deposit, with gold, silver and copper occurrences, mainly in sulphides. The deposit is related to the Miocene porphyry stocks and dikes that have been identified in the area, cross cutting the older sedimentary, igneous and metamorphic rocks.
Mineralisation
Mineralisation within the Soto Norte Project comprises parallel anastomosing veins which occupy the composite fault system. These veins have various widths and characteristics depending upon the open spaces provided by the fault movements, which occurred over time, as evidenced by multiple mineralised events recorded within the individual vein structures and host rocks.
Veins at Mascota exhibit open-space filling textures along the Mascota related structures, indicating low overburden stress consistent with a shallow crustal emplacement typical of epithermal vein systems.
Brecciation is apparently of a hydrothermal origin (angular fragments, commonly monolithic, locally with jigsaw textures and, typically fragment-supported, dominantly cemented by hydrothermal minerals) and is observed in most mineralised zones, with the common feature that the brecciated fragments consist of local wall rock.
The mineralisation has a variety of textures of cement fill that are characteristic of an epithermal environment, with colloform bands of quartz and colloform pyrite that indicate super saturation in a relatively low temperature environment.
Veining in the El Gigante structure is mostly characterised by more compact, less vuggy and often banded textures. It is also characterised by more heavily altered wallrock and clay content consistent with the veining following the La Baja Fault and where post-mineralisation fault movement has probably taken place.
Overall, the veins cover a strike extent of 2.6 km and have been drilled to a depth of approximately 800 m below the surface. The width of the veins is variable dependent on the major and minor structures, but also pinch and swell within individual structures. On average the ranges are between 1 – 30 m width. The mineralised structures extend to the surface and are open at depth and along strike, with high exploration potential to target the deep structures from underground drilling stations.
Mineralogy
Gold and occasional electrum are observed in core and under the microscope as having a strong relationship with fine, crystalline pyrite (not the coarser crystalline pyrite) and occurs either free with the gold, adhering to pyrite particles or encapsulated within the pyrite crystalline lattice. Copper sulphides appear to have a partial affinity for pyrite but have much less of an association with gold than the pyrite because of its more irregular distribution. Gold also occasionally occurs within telluride minerals like calaverite and petzite, which are rarely visibly identifiable, although their possible presence is reflected in the sporadic distribution of tellurium assays. There is also a perceived relationship with quartz. Several mineralising events which introduce quartz, each time the quartz is introduced, become darker in colour (grading from white to dark grey). The fine crystalline pyrite has an association with this, either encapsulated within the darker quartz or emplaced within the darker quartz.
Silver occurs occasionally as native silver in the shallower SW end of the explored mineralisation in the El Cuatro zone and, more frequently, as silver sulphosalts, pyrargyrite and proustite.
Copper occurs principally as enargite and to a lesser extent as bornite, chalcopyrite, primary chalcocite and tetrahedrite-tennantite. Chalcopyrite is seen as being enriched on a local scale to bornite, covellite, secondary chalcocite and finally to native copper.
Arsenic (a penalty element) is principally associated with enargite. It is rarely seen as arsenopyrite but may be attributable to the presence of tennantite.
Zinc (a potential penalty element) occurs as red to black sphalerite or wurtzite and occurs associated with the distribution of lead, principally occurring as hinsdalite and occasionally as bournonite and possibly boulangerite.
Antimony (a potential penalty element) occurs occasionally as jamesonite and tetrahedrite and on a very small scale in bournonite and boulangerite.
Bismuth (a potential penalty element) occurs as a trace element within the deposits and may be related to bismuthinite or tellurobismuthite.
Tungsten occurs mainly as hubnerite and occasionally as ferberite. Hubnerite occurs as very fine, bright red transparent needles in quartz, is seen throughout the Mascota vein and is one of the indicators that mineralisation continues to the SW towards California.
The near surface to surface oxidation zone, which has an irregular depth and penetrates much deeper around major fractures and faults, is dominated by the reduction of sulphide minerals (being mainly pyrite) to haematite and goethite and limonite. Copper sulphides in the transition zone in old workings are seen commonly reduced to chalcanthite.