Some important pyrite deposits,called“Dabaozhuang-type”pyrite deposits in this paper, are developed in the Lujiang-Zungyang continental volcanic basin.They were considered to be hydrothermal deposits related with subvolcanic rocks and associated with“porphyrite iron deposits”.But our recent study shows that they are substantially of exhalation-sedimentationhydrothermal superimposition and transformation origin.The main reasons are as followings: 1.Most pyrite deposits are located at the uper horizon of the first volcanic cycle formation, consisting of volcanic-sedimentary sequence.Ore bodies are bedded,bed-like or lenticular,having many synsedimentary structures.Microbial textures in sulfides can also be found. 2.Host rocks are mainly tuff-siliceous formation and some anhydrite beds with barite, which have been proved to be important prodt,cts of exhalative-sedimentary process. 3.The deposits are clearly zoned in their compositions,ore structures and minor elements. And zoning centers are close to volcanic apparatuses or fracture zones. 4.There exists“reverse”paragenetic sequence from lower to higher temperature minerals: anhydrite→pyrite→magnetite and hematite,being contrary to the hydrothermal sequence. 5.Inclusions in minerals are very small(<3μm)with vapor/liquid ratio less than 10%, their homogenization and decrepitation temperatures are about 100℃ and 105—140℃,respectively.The sulfur isotope composition supports the view that much sedimentary sulfur contrubuted to the deposits. 6.In assition,hydrothermal superimposition and transformation are very obvious,such as recrystallization,secondary enlargement and tr nsformation of mineral facies(e.g.pyrite to magnetite)etc..
Hu Wenxuan,Xu Keqin. STUDY ON DABAOZHUANG-TYPE PYRITE DEPOSITS——EXHALATION-SEDIMENTATION-SUPERIMPOSITION-TRANSFORMATION SULFIDE DEPOSITS IN THE LUJIANG-ZUNGYANG BASIN,ANHUI PROVINCE[J]. Chinese Journal of Geology, 1992, (3): 213-223.