STRUCTURAL AND STRATIGRAPHIC CONTROLS ON MINERALIZATION, CATALINA HUANCA POLYMETALLIC DEPOSIT, AYACUCHO PROVINCE, PERU

Mineralization in the Catalina Huanca deposit is known in lower Triassic Mitu Group molassic conglomerate, unconformably overlying middle Triassic-lower Jurassic Pucará Group carbonate, and Tertiary(?) dacitic intrusions. The deposit is localized in a structurally complex zone (folds and strike-slip and reverse faults) near the intersection of regional lineaments trending N, NE, and NW, and a series of sub-volcanic intrusions (mineralization is spatially associated with, and locally controlled by, intrusive dikes, sills, and stocks). Although regional folds trend NW, most folds in the deposit area trend NNE-SSW.

Mineralization has two main trends: NE and ENE-to-EW. Steep-dip, NE-strike veins occupy sinistral faults (oblique-reverse?), and limit the known mineralization to a NE-trending corridor. Steep-dip, EW-strike veins in the corridor occupy dextral strike-slip faults and are best developed in Mitu rocks. In Pucará carbonates, EW-strike veins splay into horsetail structures where faults change strike near the fault tip. Horsetail structures coincide with NW-dip, moderate- to low-dip mantos with replacement mineralization; some mantos contain homoclinal bedding, others contain folds, steep-dip fault-veins, and low-dip thrust fault-veins that are locally bedding-parallel, but locally cut bedding, indicating a flat-ramp thrust fault geometry. Horse blocks between fault-vein splays are variably mineralized (with both replacement and veinlet style mineralization).

We propose a structural-mineralization model in which the NE-trending mineralized corridor was localized above the magmatic center, and formed in a right-stepping contractional jog (positive flower structure) along a regional N-trending sinistral strike-slip fault system. Inside the corridor, fault blocks bounded by dextral strike-slip fault-veins moved by a bookshelf shearing process. Overturned folds and thrust faults in the deposit area indicate shortening deformation (especially in some mantos) that was synchronous with strike-slip faulting in the steeply-dipping vein systems. Ore shoot orientation models predict that dilational jog ore shoots and fault/fault-splay intersection ore shoots are nearly vertical, and that fault-bedding intersection ore shoots rake mostly west at moderate angle.