Summary:
Translated from Spanish using AI
The Tizapa Zn-Pb-Cu-Au-Ag deposit, located in southwestern Mexico, consists of mineral lenses within a volcanogenic massive sulphide system of the Kuroko type. The deposit is situated in the Guerrero terrane, a sequence of calc-alkaline volcanic arc rocks from the Late Palaeozoic to the Cretaceous, along with clastic sedimentary rocks and an overlying carbonate platform.
The stratigraphic units exposed in the deposit area include:
1. Grey phyllites of the Triassic to Jurassic Tejupilco schist, stratigraphically overlain by
2. Late Jurassic to Early Cretaceous metavolcanic rocks of the Teloloapan volcanic assemblage, and the limestones of the Middle Cretaceous Amatepec Formation.
The massive sulphide lenses occur at the stratigraphic contact between the Teloloapan volcanic assemblage and the Amatepec Formation.
The footwall metavolcanic rocks are bimodal and include a lower porphyritic sequence with plagioclase-andesitic composition and a likely upper unit of felsic tuff with highly variable thickness. Potassium feldspar megacrysts in the augen gneiss intrude the Tejupilco schist to the south of the mine, and various compositional types and ages of dikes are present in both the footwall and hanging wall of the deposit. Tertiary and Quaternary volcanic rocks unconformably overlie the deformed Mesozoic and Palaeozoic sequences. All pre-Tertiary rocks exhibit greenschist facies metamorphism associated with the Laramide orogeny.
In the municipality of Zacazonapan, at the Tizapa deposit, the host rock is a volcanosedimentary sequence with greenschist facies metamorphism. This sequence comprises graphitic phyllite with complex intercalations of chlorite-muscovite schists and carbonaceous slate. The age of this sequence is considered to range from Late Triassic-Early Jurassic to Early Cretaceous.
The dimensions of the mineralised bodies at this deposit are variable in both thickness and extent. They cover an area of approximately 500 m east-west and 400 m north-south, although there is significant potential for greater extension. These bodies are often associated with relatively large zones of disseminated sulphides. Macroscopically, dark grey and yellowish bands are commonly observed, representing sphalerite and pyrite-chalcopyrite zoning, respectively.
Tizapa is currently the most important volcanogenic polymetallic deposit in the state and one of the most significant in the country due to its grades and reserves. The numerous layers of sulphides are thought to result from the folding and thrusting of an original single layer deposited over andesitic to dacitic rocks. These rocks, through hydrothermal alteration and metamorphism, transformed into the current sericite and biotite schists and were subsequently overlain by carbonaceous shales, now converted into graphitic schists.
As a characteristic deposit of this region, Tizapa is composed of three stratiform, lenticular massive sulphide bodies concordant with the foliation of the host rock. The deposit formed through the exhalation of hydrothermal fluids below the seafloor. These fluids traveled through fractures, transporting Fe, Zn, Pb, Cu, As-rich sulphides, and Ag sulfosalts.