Summary:
The Project mineralized zones are considered to be typical of mesothermal vein-style, or orogenic-style gold deposits.
Orogenic gold deposits occur in variably deformed metamorphic terranes formed during Middle Archaean to younger Precambrian, and continuously throughout the Phanerozoic. The host geological environments are typically volcano–plutonic or clastic sedimentary terranes, but gold deposits can be hosted by any rock type. There is a consistent spatial and temporal association with granitoids of a variety of compositions. Host rocks are metamorphosed to greenschist facies, but locally can achieve amphibolite or granulite facies conditions.
Gold deposition occurs adjacent to first-order, deep-crustal fault zones. These first-order faults, which can be hundreds of kilometres long and kilometres wide, show complex structural histories. Economic mineralization typically formed as vein fill of second- and third-order shears and faults, particularly at jogs or changes in strike along the crustal fault zones. Mineralization styles vary from stockworks and breccias in shallow, brittle regimes, through laminated crack-seal veins and sigmoidal vein arrays in brittle-ductile crustal regions, to replacement- and disseminated-type orebodies in deeper, ductile environments.
Mineralization can be disseminated, or vein hosted, and displays a timing that is structurally late, and is syn- to post-peak metamorphic. Quartz is the primary constituent of veins, with lesser carbonate and sulphide minerals. In volcano-plutonic settings, pyrite and pyrrhotite are the most common sulphide minerals in greenschist and amphibolite grade host rocks, respectively.
Gold is usually associated with sulphide minerals, but can occur as free gold. Gold to silver ratios typically range from 5:1 to 10:1 and, less commonly, the ratios can reach 1:1.
Alteration intensity is related to distance from the hydrothermal fluid source, and typically displays a zoned pattern. Scale, intensity, and mineralogy of the alteration are functions of wall rock composition and crustal level. The main alteration minerals can include carbonate (calcite, dolomite, and ankerite), sulphides (pyrite, pyrrhotite or arsenopyrite), alkali-rich silicate minerals (sericite, fuchsite, albite, and less commonly, K-feldspar, biotite, paragonite), chlorite, and quartz.
The larger examples of orogenic deposits are generally 2 km to 10 km long, about 1 km wide, and can persist over 1 km to 2 km vertical extents.
Deposit Descriptions
Mineralization has been identified over approximately 1.8 km of strike length within the Project area, and was subdivided into four fault-bounded zones referred to as Los Planes, Intermediate, Las Colinas, and La Colpa.
Local normal and listric faulting displaces and truncates the mineralized zones (Herdrick, 2009). Drilling suggests that a northwest-trending graben basin has displaced the Los Planes deposit by more than 200 m, over increments of 20–100 m. These blocks are bounded by listric faulting and are dropped en echelon down to the northeast along N40W-trending structures. Much of the outcrop is covered by pediment that thickens to the east, featuring cobbles and boulders of schist and gneiss.
Los Planes
Mineralization extends along a north–south strike length of approximately 975 m. Drilling has encountered continuous mineralization to depths of 400 m from the surface. Mineralized lenses average 90 m in thickness. Mineralization thickness is highly variable due to the stockwork-style of mineralization, and zones can locally coalesce into broader intervals >100 m in thickness. Mineralization is interpreted to remain open along strike to the north and at depth.
Las Colinas
The mineralized zone has a roughly north–south strike and dips at about 50º to the west. The zone is 675 m long, averages 40 m thick, and extends to a depth of 250 m. The zone remains open at depth, but is limited to the north, where it is interpreted to end where a northwest-trending fault intercepts the strike of the mineralization.
Intermediate
The zone is hosted within a shear zone that strikes approximately north–south and dips at about 50º to the west. Mineralization extends along strike for about 900 m in this fault block and zones are 45 m in thickness on average. Drilling has intercepted continuous mineralization to about 325 m depth. Mineralization is truncated to the north and south by west–northwest-trending faults that that separate the zone from the Los Planes and Las Colinas zones, respectively. Despite being limited on strike, the Intermediate zone remains open down dip to the west.
La Colpa
The mineralized zone has a roughly north–south strike and dips at about 35º to the west. The zone is 625 m long, averages 60 m thick, and extends to a depth of 250 m. The zone remains open down dip and along strike to the south.