The San Agustin complex is owned and operated by Minera Real del Oro, S.A. de C.V., which is a wholly-owned Heliostar Metals Ltd subsidiary.
Heliostar announced notice of the acquisition of the Mine on July 17, 2024, from Florida Canyon Gold Inc., an interim successor to the former operator Argonaut Gold Inc., and completed the acquisition on November 8, 2024.
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Summary:
The San Agustin mine and the El Castillo mine together form the San Agustin Complex.
San Agustin
The San Agustin Project is located in Northwest Mexico in the east flank of the Sierra Madre Occidental (SMO) bordering the great Mesa Central Mexicana. The oldest rocks in the region are mica schists and mylonites. These are overlain by an Upper Jurassic to Lower Cretaceous sedimentary flysch sequence mainly composed of an alternating sequence of shale and fine-grained sandstone with occasional horizons of calcareous shale and thin layers of limestone.
The volcanic complex of the SMO is present in the area. The Lower Volcanic Complex occurs as agglomerates, tuffs, and andesitic flows. The Upper Volcanic Complex consists of a sequence of rhyolite tuffs, crystal tuffs, and ash tuffs. Discordantly covering all previously mentioned lithological units is a package of welded rhyolite tuffs. The most recent igneous unit observed is composed of Pleistocene vesicular basalt flows that cover some of the valleys to the southeast of the Project.
There is a widespread occurrence of a poorly consolidated conglomerate that fills wide valleys associated with basin-and-range extensional normal faulting. A quartz monzonite stock, a biotite-rich volcanic rhyolite dome, and a package of ash and crystal tuffs also occur in the region.
Two main structural trends were identified in the San Agustin area. Although Mineralization at the Project appears to be related to or associated with the northeast-trending structures, geophysical data shows anomalies aligned with the northwest-trending faults and fractures.
The most obvious structure recognized on the Project is the Main Fault, which trends northwesterly and dips steeply to the southwest.
The area of known mineralization at the San Agustin Project is dominated by an igneous, quartz monzonite dome complex intruding a clastic sedimentary sequence composed of shale, mudstone, and less abundant sandstone. Both the intrusive complex and the sedimentary sequence occur on a dominant northwest trend with sub-vertical dips. Mineralization is emplaced through a strong and widespread system of sulphide rich veins, veinlets and fissure fillings that make the system similar to a disseminated deposit. Locally, mineralization can be observed following lithological controls in the sedimentary rocks, especially where they run parallel to sediment-intrusive contacts. The most dominant alteration type is phyllic, characterized as an assemblage of sericite-quartz-pyrite mineralization.
Mineralization
The host rocks for mineralization at San Agustin are quartz monzonite-dacite bodies and the sedimentary sequence they intrude. Mineralization is emplaced through a strong and widespread system of sulphide rich veins, veinlets, and fissure fillings that make the system similar to a disseminated deposit. Fracture systems follow two main project-scale trends that run northeast and northwest. Locally, mineralization can be observed following lithological controls in the sedimentary rocks, especially where they run parallel to sediment-intrusive rock contacts. Mineralization is also observed in the flow facies of the intrusion and is usually characterized by disseminated pyrite and in parallel veinlets. A component of the pyrite is thought to be pre-mineralization and associated with early phyllic alteration. The mineral system has very little silica and is more related to sulphide fracture filling. Epithermal boiling textures were observed locally such as bladed textures, coliform silica, or drusy quartz. These epithermal textures are not common. Some structures with cryptocrystalline jasperoid have also been found in deeper drill intercepts within sulphide zones. Two late phases of mineralization were identified with one carrying sphalerite and pyrite, and the other, galena and sphalerite. This mineralization is related to an epithermal low sulphidation system superimposed over the intrusion-related gold system.
The Main Fault, an important northwest striking and westerly dipping post-mineral fault, bisects the mineralized area showing differences in mineralization on either side. On the hanging-wall (west side) it is common to find structures rich in manganese and barite that are not observed in the footwall. The hanging-wall block also has higher silver and lead grades than the footwall block.
The sulphide boundary is located within a range of 30 m to 170 m below the surface with an average depth of about 65 m. The boundary is reached when the rock colour turns grey and disseminated pyrite becomes visible. The transition zone is commonly less than 1 m wide. The boundary’s surface is undulating and erratic across the deposit, due to the many faults and fractures controlling ground water in the area.
Deposit Descriptions
The San Agustin deposit is roughly 1,500 m long by 800 m wide. The average depth of oxide material is 65-100 m below surface. Gold mineralization is found along faults and fractures within the host igneous and sedimentary rocks and as disseminations in halos across the deposit. Sulphide mineralization extends, where drilled, down to an average depth of about 200 m with the deepest tested areas extending to 400 m below surface.
El Castillo
El Castillo is interpreted to be a porphyry-style gold system related to Eocene granodiorite– diorite porphyries that intrude Cretaceous clastic and carbonate sediments in an extensional tectonic setting. Gold mineralization occurs throughout the magmatic-hydrothermal system in space and time and is related to sulphide mineralization spatially associated with early potassic development and genetically related to an overprint of phyllic alteration. Supergene alteration, formed as a product of acid leaching, has resulted in argillic-quartz alteration assemblages within the oxide zone of the deposit. The main gold event is believed to be associated with magmatic hydrothermal fluids corresponding to phyllic alteration.
Mineralization
The moderately dipping granodiorite–diorite sills, siltites and argillites are the most favourable host lithologies. Argillic–quartz alteration is often closely associated with the intrusive contacts and can be indicative of higher-grade zones of mineralization.