The zoning rule and forming mechanism of tectonite-mineralized alteration lithofacies of black/fracture zone of the Daliangzi Pb–Zn deposit in southwest Sichuan in China

Abstract

As one of the typical deposits in the Sichuan-Yunnan-Guizhou Pb–Zn metallogenic province, the Daliangzi Pb–Zn deposit has a close genetic relationship with the structural system of the black/fracture zone formed under the action of the NWW-approximately EW strike-slip structures in the metallogenic province. The R1 black/fracture zone has a close relationship with ore forming; however, the mechanism of the rock- and ore-controlling action of the structural system remains unclear. Based on a detailed analysis of the tectonite-mineralized alteration lithofacies of the R1 black/fracture zone, the tectonite-mineralized alteration lithofacies zones can be divided into four types in succession outward from the Pb–Zn mineralization center (F₅, F₁₀₀, and other faults), i.e., (1) the brecciated and stockwork-like Pb–Zn mineralization-complex breccia facies zone; (2) the stockwork-like Pb–Zn mineralization-simple breccia and cataclasite facies zone; (3) the veined pyrite–sulfide–dolomitic cataclasite facies zone; (4) the fine-veined calcite-black carbonized dolomite facies zone. With the evolution of the ore-forming fluid, the homogenization temperature decreases from Zone 1 to Zone 4; the salinity increases from Zone 1 to Zone 2 and then it decreases from Zones 3 and 4. The fluid density shows little change overall. The contents of Zn, Pb, Cu, Ga, Ge, Cd, Ag, and other metallogenic elements, Zn/Pb ratio, and CaO/MgO mole ratio decrease gradually from Zone 1 to Zone 4, and the REE fractionation, calcilization, silicification, and pyritization enhance gradually from Zone 1 to Zone 4. This series of changes is the product of diapirism (cryptoexplosion) of strike-slip structures and the black/fracture zone, among which the second-order structures derived from NWW-approximately EW-striking dextral shear-tension faults F₁ and F₁₅ control the brecciated and stockwork-like Pb–Zn mineralized complex breccia facies zones and the stockwork-like Pb–Zn mineralized simple breccia and cataclasite facies zones. Therefore, this paper establishes the zoning mode of tectonite-mineralized alteration lithofacies of the black/fracture zone and proposes that Zones 1 and 2 provide important prospecting criteria.