In March 2022, Hochschild established a new Canadian company, Tiernan Gold Corp (Tiernan), and on 14th March 2023 completed a restructuring where Tiernan became 100% owner of Andina Minerals Chile SpA and a subsidiary of Hochschild UK.
Andina Minerals Chile SpA is owner of Volcan Project.
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Summary:
The structural setting of the Volcan property is related to, and associated with, the formation of the Copiapo stratovolcano (Volcan Copiapo) and may also be related to regional northerly-trending high-angle reverse faulting. Cameco originally identified three generally moderate to steeply dipping fault systems, trending northwest-southeast, northeast-southwest and east-west, and considered the northeast-southwest and east-west trending systems to be the more important structural controls on alteration and mineralization.
The principal rock types identified on the Volcan property are:
• Dacite, rhyodacite and andesite lavas;
• Volcanic flow and dome complex rocks;
• Pyroclastic flows;
• Hydrothermal breccias;
• Sub-volcanic porphyry.
Gold-copper mineralization at Volcan is related to the intensely developed hydrothermal alteration that gave rise to the native sulphur deposits in the area. The hydrothermal system was a consequence of the sub-volcanic intrusion of dacitic to microdioritic porphyry into a complex of domes and lava flows of dacitic composition.
Mineralization
Easdon (2005) describes the gold mineralization as follows:
“The generation of this sulphur [i.e., the native sulphur], with associated and anomalous mercury, arsenic, antimony and gold, was recognized (Zentilli, 1990) to be related to near-surface, but deeper seated multiple hydrothermal high sulphidation epithermal systems which are developed in a complex of domes and lava flows of dacitic composition. The hydrothermal system(s) are considered to be related to sub-volcanic intrusion of dacitic to (micro)-dioritic porphyries into the volcanic dome complex. These systems have resulted in (probably) several episodes of very high-level acid leaching of the host rocks (with the resultant advanced argillic and argillic-silicic style of alteration) and the development of quartzalunite-gypsum, as well as silicified vents with hydrothermal explosion breccias which may be impregnated with sulphur. Gold-(copper) mineralization, which occurs at some depth (dependent on the degree of telescoping of the system) below the surface manifestation of the solfataric systems, is “often identified in “swarms” of banded quartz veinlets” and which may occur “within transitional potassic-argillic altered rock” (Bartlett, 2004). Magnetite (partially to totally martite-altered) and secondary biotite are also described as alteration products (Geoexploraciones, 2003). Lower grade gold mineralization appears to be related to a phase of disseminated sulphide (primarily pyrite) mineralization which is typically associated with an argillic-silicic alteration.”
“The mineral occurrences in the Dorado Sector of the Volcan Property comprise a combination of primarily gold bearing quartz-sulphide (predominantly pyrite) veinlets with peripheral lower (< 0.5 g/t Au) grade gold associated with disseminated pyrite developed in largely advanced argillic-silica altered fragmental tuffaceous and porphyritic dacitic volcanic, as well as in dacitic dome complex rocks. Similar style mineralization is encountered in ODAE in which exploration was initiated in 2006. The mineralization is variously hosted in (or intimately related to) silicified hydrothermal breccias, in the permeable tuffs and otherwise previously prepared and permeable altered volcanics, and in dacitic dome breccias which may have formed peripheral to the dome cores. These occurrences are associated with the + 8-10 Ma Miocene formation and subsequent partial destruction of the Volcan Copiapo stratovolcano and related sub-volcanic intrusive events which are responsible for the extensive and widespread high-level hydrothermal (high sulphidation epithermal style) alteration and mineralization. The mineralization is contained within the altered dacitic rocks and is associated with faults, hydrothermal breccias and brecciated dome boundaries. The location of the mineralization in part appears to be controlled by the dilational (jog) structures and in part by the permeability/porosity of the dacitic tuffs, including previous alteration events. Andina Chile geologists have constructed graphs of the available drill hole geochemistry and have determined that the metal correlations are more characteristic of Au-Cu-Mo porphyry type mineralization than the metal correlations are for an epithermal type of mineralization for the Dorado Sector. Although Au and As at shallow depths are closely correlative, this correlation appears to fall off/dissipate with depth; mercury has a weak correlation with both Au and As.”
The Volcan property covers the Dorado sector (Dorado Este, Central and Oeste zones, of which the latter has been subdivided into the Oeste Norte and Oeste Sur zones) and ODAE which lies to the northeast of Dorado. The following descriptions of the Dorado deposits have been summarized from Easdon (2005). The mineralized zones, at the moment, are defined by mineralized grade cut-off to constrain the extent of the mineralization and this may be subject to change depending on the interpretation of the mineralization by a QP. Therefore, as the Project is advanced the boundary of the deposits may be subject to change as further information is acquired or the geological interpretation is altered.
Dorado Este (DE)
“The Dorado Este mineralization and deposit is contained within dacitic tuffs and dacite porphyries which show extensive advanced argillic and argillic-silica alteration and with the development of a generally centrally located irregularly shaped, hydrothermal breccia pipe. Initial geological mapping indicates that the mineralization is grossly banded in an east-west sense and that the mineralization dips steeply to sub-vertically. The emplacement of the mineralization may be in part controlled by the intersection of WNW and NNW steeply dipping structures; the NNW structures may be terminating, or down dropping, the mineralization on both the east and west sides of the >0.2 g/t Au geochemical anomaly which defines the Dorado Este area. The western extension of the mineralization may also be partially limited by a post-mineral intrusive which is located approximately 200 m to the west of currently [i.e., in 2005] defined western limit of the deposit.”
Dorado Central (DC)
“The Dorado Central zone is hosted by the same rocks and has undergone similar alteration to that seen in the Dorado Este zone. Host rocks to the mineralization comprise dacitic domes and dacitic tuffs and dacitic porphyry flows with the accompanying and localized development of hydrothermal breccias. The geochemical sampling that has been done in this zone [i.e., to 2005] indicates that this zone is apparently part of the roughly east-west dilational jog zone as seen at Dorado Este but which is offset approximately 600 m to the SW of the Dorado Este zone and is located approximately 200-300 m west of Dorado Este.”
Dorado Oeste (DO)
“The Dorado Oeste zone is defined by what is an essentially northerly (NNE) trending somewhat discontinuous geochemical anomaly (>0.2 g/t Au) which is approximately 1.75 km long (N-S) and up to 500 m wide. Dorado Oeste is predominantly underlain by dacticic tuffs and porphyries and has apparently been intruded by at least two variably continuous NE trending dacitic dikes.”