Summary:
The Panuco Project is on the western margin of the Sierra Madre Occidental (SMO), a high plateau and physiographic province that extends from the U.S.A.–Mexico border to the east-trending Trans-Mexican Volcanic Belt.
The structure of the Project area is dominated by north-northwest-trending extensional and transtensional faults developed or reactivated during the Basin and Range tectonic event (~28 to 18 Ma).
Deposit Model
Mineralization in Panuco occurs in veins and mantos with mineralogical characteristics, alteration assemblages, temperature, and salinities typical of low to intermediate sulfidation epithermal deposits. Because of the region's long and complex deformation and hydrothermal history, the Panuco Project has the potential to host other deposit styles. Late Cretaceous to Paleocene batholiths that intrude the Tarahumara Formation rocks in Panuco, are prospective for porphyry copper and molybdenum deposits elsewhere in the SMO. Late Cretaceous - Eocene plutons that intrude basement metasediments and limestones are prospective for gold-rich and polymetallic skarns and replacement deposits. However, the mineralized structures that are exposed and that have been explored to date in the property are only the epithermal silver and gold veins that were developed or reactivated during the extensional tectonics of the SMO volcanic arc
Mineralization
Mineralization on the Panuco Property comprises several epithermal quartz veins. Previous workers and recent mapping and prospecting works conducted by Vizsla´s geologists determined a cumulate length of veins traces of 86 km. Individual vein corridors are up to 7.6 km long and individual veins range from decimetres to greater than 10 m wide. Veins have narrow envelopes of silicification, and local argillic alteration, commonly marked by clay gouge. Propylitic alteration consisting of chlorite–epidote in patches and veins affecting the andesites and diorite are common either proximal or distal to the veins.
The primary mineralization along the vein corridors comprises hydrothermal quartz veins and breccias with evidence of four to five different quartz stages: generally white, grey and translucent and varying grain size from amorphous-microcrystalline-coarse. A late stage of amethyst quartz is also observed in some veins. The grey color in quartz is due to the presence of fine-grained disseminated sulfides, believed to be mainly pyrite and acanthite.
Vizsla has defined several hydrothermal breccias with grey quartz occurring more commonly at lower levels of the vein structures. Barren to low grade, quartz is typically white and is more common in the upper parts of the veins and breccias. Locally, mineralized structures are cut by narrow, banded quartz veins with thin, dark argentite/acanthite, sphalerite, galena, and pyrite bands. Bladed and lattice quartz pseudomorphs after calcite have been noted at several locations within the veins and indicate boiling conditions during deposition. Later quartz veinlets cut all the mineralized zones with a mix of white quartz and purple amethyst. The amethyst is related to mixing near-surface waters as the hydrothermal system is collapsing, as has been noted in the nearby San Dimas district (Montoya–Lopera et al., 2019).
The Mineral Resource includes eleven mineralized vein systems: the Napoleon, Napoleon hanging wall, Josephine, and Cruz Negra veins; the Copala, Cristiano, Tajitos and Copala 2 veins; the San Antonio vein; and the Rosaritos and Cuevillas veins. These trends are west to east within the Napoleon, Cinco Senores, Cordon del Oro, and Animas-Refugio corridors. The bulk of the resource veins strike north-northwest to north-northeast, with thicknesses varying from 1.5 m to over 10 m.
Structural Controls
Mineralized structures in Panuco resulted from a long history of deformation accompanied by multiple hydrothermal mineralization events spanning from the late-Laramide orogeny to the Basin and Range extension. Multiple deformation events resulted in west-northwest thrusts and conjugate north-northwest to north-south dextral and east-northeast sinistral shears that were developed during the two peaks of the Laramide compressional orogeny. Some of these older structures served as well as conduits for the emplacement of porphyry type deposits in western Mexico. The Laramide age main thrust and conjugate faults were subsequently reactivated during post-Laramide extensional events during the late-Eocene, Oligocene, and Miocene.
Therefore, structures like Napoleon and Copala originated as late-Laramide conjugate shears that were reactivated and opened to the fluid passage and epithermal mineralization during the Laramide extensional deformation D3 event. Steeply dipping structures, the conjugate components to the low angle thrust shears, were also reactivated during post Laramide extension and some of them were mineralized as well. Napoleon is interpreted to be a reactivated conjugate sinistral shear.
During post Laramide extension, events D3, D4 and D5, occurred significant block faulting and tilting. Some of this faulting and tilting occurred concomitant or after mineralization, thus segmenting or tilting mineralized structures. A clear example of this tilting occurs in Napoleon, where infill and step-out (expansionary) drilling conducted during 2021, supported by geological and geochemical interpretations (alteration and metal zonation) confirmed that the Napoleon vein system is tilted to the south, with the southern extent being at the top of the mineralized horizon near surface.
Copala on the other hand, is a low-angle dipping structure bounded to the west by the steep dipping Tajitos and Cristiano veins that also shows variable dip angle from shallow (35°) in the north to moderate (55°) in the south. Because there is a significant component of strike-slip displacement imposed on most structures, pinching and swelling is common.
Tajitos is interpreted as a conjugate shear, and according to Starling (2019), it exhibits an early sinistral transpressional shear sense overlapped by a dextral tensional shear sense. The diorite stock emplaced along an east-northeast trending central fault zone that likely originated during the early-Laramide deformation. Many of the structures hosted by the diorite appear to have better continuity than those hosted by the andesites and rhyolitic volcanics.