Summary:
The Property is located within the Western Cordillera of the Andes Mountains and the regional geology is dominated by Cretaceous aged Machay Group limestones and Tertiary aged Pocobamba continental sedimentary rocks, which are referred to as the Casapalca Red Beds.
These groups have been deformed by the Huaron anticline, the dominant structural feature of the local area. The limestones and sedimentary rocks are strongly folded and intruded by quartz monzonite and quartz monzonite dikes with associated fracturing. Following the intrusion of the dikes, the sedimentary rocks were further compressed and fractured, and subsequently altered and mineralized by hydrothermal fluids forming the Huaron deposit on the Property.
The main lithology in the area of Huaron is a sequence of continental redbeds of the Casapalca Formation which unconformably overlie massive marine limestones. A series of andesites and dacites outcrop to the west of the mine. North-south trending sub-vertical porphyritic quartz monzonite dykes crosscut the mine stratigraphy.
Thinly bedded marls and sandstones known as the lower redbeds are present in the central part of the mine and at lower elevations. The upper redbeds are present on the eastern side of the mine, and are comprised of calcareous chert overlying sandstone and marls, in turn overlying the Barnabe quartzite conglomerate at the base of the sequence. On the western side of the mine, the stratigraphy consists of a series of interbedded conglomerates and sandstones.
The Huaron deposit is located within an anticline formed by east-west compressional forces. The axis of the anticline strikes approximately north-south and plunges gently to the north. There are two main fault systems. One system comprises north-south striking thrust faults, parallel to the axis of the anticline, and the other comprises east-west striking tensional faults.
Mineralization
The Huaron mine is a producer of silver, zinc, lead, and copper. Ore mineralogy is made up of tetrahedrite - tenantite (gray copper), sphalerite, galena, and chalcopyrite - enargite as the most abundant ore minerals; gangue minerals mainly represented include quartz, rhodochrosite, rhodonite, manganocalcite, and alabandite.
Research has shown the presence of three different stages of mineralization and related to high temperatures (milky quartz, pyrite, tetrahedrite), intermediate temperatures (milky quartz, pyrite, brown sphalerite, and galena) and low temperatures (barite, siderite, dolomite, blonde sphalerite, galena, argentiferous tetrahedrite, polybasite, chalcopyrite, rhodochrosite, quartz, and calcite). Huarón mineralization is assumed to be of Pliocene age.
The first pulse of mineralization was associated with the emplacement of intrusive bodies and the subsequent opening of structures, as zinc, iron, tin, and tungsten minerals were deposited. This was followed by a copper, lead, and silver rich stage, and finally by an antimony / silver phase associated with quartz.
The most important economic minerals are tennantite-tetrahedrite (containing most of the silver), sphalerite, and galena, though more than 90 other minerals have been identified. The principal gangue minerals are pyrite, quartz, calcite, and rhodochrosite. Enargite and pyrrhotite are common in the central copper core of the mine and zinc oxides and silicates are encountered in structures with deep weathering. Silver is also found as pyrargyrite, proustite, polybasite, and pearceite.
There is a definite mineral zoning at Huaron. A central copper core contains enargite as the principal economic mineral with copper, pyrite and quartz in structures. This area was extensively mined by previous operators but metal grades and prices were overshadowed by the negative impact of high arsenic and antimony content and poor metal recoveries. To the east and west of the central core silver, lead, and zinc minerals are associated with calcite and rhodochrosite. Areas to the north of the central core contain silver, lead, and zinc minerals associated with pyrite. Sphalerite and sulfosalts with rhodochrosite follow a narrow band running north-south along the general axis of the anticline.
Huaron is a hydrothermal polymetallic deposit of silver, lead, zinc, and copper mineralization hosted within structures likely related to the intrusion of monzonite dikes, principally located within the Huaron anticline. Mineralization occurs in veins parallel to the main fault systems, in replacement bodies known as “mantos” associated with the calcareous sections of the conglomerates and other favorable stratigraphic horizons, and as dissemination in the monzonitic intrusions at vein intersections. The mineralization controls recognized in the deposit are structural, lithological, and stratigraphic.
The types of mineralized bodies present in Huarón are veins, mantos, and stockworks.
Veins: The mineralized veins vary from a few cm to up to 10 m wide, and may extend along strike for up to 1,800 m. Most of the structures show open mineralization at depth and along strike and have excellent exploration potential. Vein orientations vary but generally trend east-west or north-south. The deposit consists of 96 different structures which have been grouped into 13 families of mineralized trends according to location and orientation.
Mantos: Mantos are gently dipping structures located on the western flank of the anticline.
Stockworks: Stockwork zones have been mined with mechanized methods and high productivity. Stockwork zones occur at the intersection of veins, where veins intersect conglomerate beds (causing replacements), and also at the intersection of veins with calcareous sandstone strata (causing disseminations). Stockwork-like bodies related to the intrusive-sandstone contact are rarely recognized.