Hydrothermal dolomitization in Dengying Formation, Gaoshiti-Moxi area, Sichuan Basin, SW China

The formation conditions, existence evidence, modification modes and timing of hydrothermal dolomitization in the Sinian Dengying Formation are studied based on the basic geological conditions, mineral assemblages in dolomites, and geochemical features of the Gaoshiti-Moxi area in the Sichuan Basin. The Gaoshiti-Moxi area is a significant exploration target of the Sinian Dengying Formation in the Sichuan Basin and has the basic conditions of regional geology for the occurrence of structurally controlled hydrothermal dolomitization: (1) activity of extensional basement-fault; (2) deep-burial hydrothermal reservoirs; (3) the overlying seal strata. Based on the petrographic analysis and geochemical tests (trace elements (Fe and Mn), stable isotopes (C, O, and Sr), homogenization temperature of fluid inclusions, etc.) of the core samples of the Dengying Formation in the study area, combing with the MVT mineral assemblages and geochemical characteristics, the study demonstrates that structurally controlled hydrothermal dolomitization exists in the Dengying Formation of the study area. This type of hydrothermal dolomitization refers to transformation of matrix dolomites by hydrothermal fluids and it consists of three modes: (1) dissolution and cementation; (2) recrystallization and neomorphism; (3) hydrofracturing. It is inferred that there exists multi period of hydrothermal dolomitization, namely, Late Sinian to Early Cambrian, Late Devonian and Late Permian.