Summary:
Deposit Types
The mineralized zone is characterized by a low-sulphidation epithermal system containing silica veins, stockworks, and breccias. These zones are generally formed in felsic subaerial complexes in extensional strike slip structural settings. Low sulphidation gold deposits are associated with magmas where ore deposition occurs several kilometres above the intrusion, and display certain alteration assemblages (Cooke & Simmons, 2000). The intrusions are likely the result of tectonic activity, such as plate subduction and extension. Deep hydrothermal fluid flow systems comprised of meteoric water, as well as near surface systems such as hot springs, are the sites of mineralization. Mineral deposition takes place as the fluids undergo cooling by fluid mixing, boiling and decompression (Cooke & Simmons, 2000).
Mineralization
Gold and silver mineralization occur predominantly along three northwest to west-northwest oriented silicified structural corridors that form a horsetail-like structural complex that ultimately all merge together towards the west. These mineralized structural corridors are named after the mineralized areas that they host, which include: 1) the Mariposa- ZapoteTahonitas (Z-T) trend; 2) San Miguel-Noche Buena (Central) trend; and 3) the Guadalupe (Guadalupe) trend. Several subsidiary mineralized structures have been identified between the main mineralized structures (Las Primas & Fresnillo). Gold and Silver values are associated with different pulses of quartz exploiting the same structure. Types of quartz are white, grey or greenish in colour, displaying classic low sulphidation epithermal textures such as saccharoidal, drussy, crustiform, colloform and crystalline textures.
Mariposa-Zapote-Tahonitas (Z-T) Trend
The Mariposa-Zapote-Tahonitas (Z-T) structure strikes to the north-northwest and dips at approximately 50° to the southwest. This trend shows evidence of previous workings, such as stopes, trenches, and adits.
Mariposa is the northernmost portion of the Z-T mineralized trend and has a length of approximately 1100m. The structure at Mariposa is at the contact between andesite and granodiorite with the rhyolitic stock. This structure is exposed on surface intermittently along the road that provides access to the historical mine workings (L?pez, 2009). Mineralization is associated with hydrothermal breccias (Turner and Hunter, (2020).
Zapote, which is divided into the North and South, is drill tested and is approximately 1.6 km in length and widths vary from 7 m to 66 m (Table 7-1). The hanging wall mineralization of Zapote is gradual and consists of quartz veining, brecciation, moderate silicification and argillization. Mineralization along the footwall is variable and consists of weak silicification and propylitic alteration. Mineralization within the main zone is strongly associated with silicified breccia and contains quartz, calcite, and adularia veins (L?pez, 2009; Turner and Hunter, 2020).
Tahonitas, which is southernmost along the mineralized trend, is approximately 950 m in length. The widths vary from 15 m to 45 m. The mineralized structure at Tahonitas dips between 45° and 60° to the southwest (L?pez, 2009). Tahonitas is hosted at the contact between rhyolite dikes and andesites of the Lower Volcanic Sequence.
San Miguel-Noche Buena (Central) Trend
The San Miguel West, San Miguel East and Noche Buena areas occur along a regional northwest – southeast striking structure called the Central trend that moderately dips between 50° and 70° to the southwest. The San Miguel West and East areas have a combined length of approximately 1,450 m and widths vary from 9 m to 75 m. This trend also shows evidence of previous workings, such as stopes, trenches, and adits. The host rocks in the area are andesites of the Lower Volcanic sequence that were subsequently intruded by an argillic altered feldspar-hornblende-biotite porphyry dike. The mineralized zone is associated with the brecciated zones proximal to the dike, as well as along the structure (L?pez, 2009; Turner and Hunter, 2020).
The Noche Buena zone is the southernmost extension of the Central trend and is hosted in a system of sub-parallel quartz veins and veinlets. This zone has an approximate length of 700 m and widths vary from 12 m to 55 m (Turner and Hunter, 2020).
Guadalupe Trend
The Guadalupe trend, which bifurcates to the east from the San Miguel West deposit, is subdivided into the Guadalupe East and Guadalupe West deposits that are separated by the “6 de Enero” claim. The trend, which has an east-west orientation, is strongly silicified and contains zones of silica stockworks. Guadalupe East and Guadalupe West have a cumulative length of 2,500 m and a true width that varies from 4 m to 68 m. The area was previously mined, with significant underground working that extend laterally by approximately 1.5 km and vertically to 400 m. The host rocks to mineralization are intermediate volcanics (Guadalupe West this is andesitic flows and tuffs, while in Guadalupe East it is predominantly feldspathic porphyry) of the Lower Volcanic sequence.
In Guadalupe East the main structure contains a steeply south dipping to vertical vein called Estaca which has seen historical mining. North dipping antithetic structures in the hanging wall of the Estaca vein are present within a 500 m long block bounded by 2 northwest structures. This block was historically called Laija and more recently Prime has described it as a “flower structure”. East of Laija there are north dipping antithetic structures in the footwall of the Estaca vein; the larger antithetic veins were called San Manual and San Nicolas and these also reported historical mining.
Additional Mineralized Areas
Two mineralized areas named Fresnillo and Las Primas occur along subordinate subparallel structures to these main structures described above. Fresnillo is located between the Z-T and Central structures and the host rocks to mineralization are rhyolitic and dacitic rocks. In Las Primas, which is east of the Central structure and south of the Guadalupe structure, the host rocks are andesites of the Lower Volcanic sequence that were subsequently intruded by a feldspathic porphyry and rhyolite/dacite intrusives.
Additional mineralized areas are also identified to the north and northeast of the main area of mineralization. These mineralized areas include Palmitas, La Verde, Las Agujas, Orito, and Mina.