Geological and geochronological constraints on the formation of the Jurassic Maozaishan Sn deposit, Dayishan orefield, South China

摘要

The Dayishan orefield in the central Nanling belt is one of the most important Sn districts in South China. Within this district, there are more than seven medium-to-large Sn, Sn-Cu and Pb-Zn-Sn deposits. The mineralization is associated with altered granites and greisen-quartz veins, both of which occur in the inner part of the Dayishan granite batholith. Cassiterite is the principal ore mineral, accompanied by subordinate molybdenite. Cassiterite separates from altered and mineralized granite and greisen-quartz veins have concordia ages of 156.5 +/- 2.8 Ma (MSWD = 3.1) and 158.0 +/- 1.8 Ma (MSWD = 1.4), respectively. Molybdenite separates from molybdenitequartz veins that crosscut the greisen alteration have a Re center dot Os isochron age of 157.9 +/- 7.7 Ma (MSWD = 26), whereas zircon separates from the porphyry monzogranite have a U-Pb age of 156.3 +/- 1.2 Ma. These ages are identical within the analytical error and, together with the field relationships, provide tight constraints on the Sn mineralization at around 156 Ma. Rhenium contents of the molybdenite suggests that the ore-forming materials were derived from a crustal source, whereas S and Pb isotopic data point to mixed sources. We suggest that the Maozaishan deposit was formed by intrusion of the related pluton, and occurred in the Late Jurassic during a period of lithospheric thinning and crustal extension of the South China Block.