ON THE OCCURRENCE OF CARBONIFEROUS VOLCANICS AND ORIGIN OF THE COPPER AND TUNGSTEN DEPOSITS OF THE FENGLIN DISTRICT,DONGXIANG,JIANGXI
Zhu Jinchu Zhang Chenghua
Through detailed field and laboratroy studies, it is found that in the Fenglin mining district and its vicinities, Dongxiang, Jiangxi, volcanics occur in the Zishan formation of lower Carboniferous age and in the lower part of the Huanglung limestion formation of Middle Carboniferous age. They comprise dacite, rhyolite lavas, and acid to acid-intermediate tuff, tuff-breccia, and tufaceous sediments, with a total thickness of more than 20 meters. Interbedded with these chiefly submarine volcanic beds and other marine sediments, are stratiform pyritic copper beds, consisting chiefly of pyrite, melnikovite, siderite, chalcopyrite, and some sphalerite and galena, which attain a total thickness of some 28 meters, and constitute a mediumsized copper mining district. Above the pyritic copper beds, occur siliceous hematite beds of some 13 meters in thickness, succeeded by chert beds and ferruginous flint of 20—30 meters in thickness, The entire succession in by Huanglung limestone. Most of siliceous hematite beds are tungsten-bearing and those considered to be low-grade tungsten ores measuring some 8 meters in thickness. Tungsten occurs mainly as absorbed ions the ferric oxide layers, averaging about 0.3—0.4% WO_3. Only through later recrystallization accompanied with some intrusive apophyses of granodiorite porphyry, does it occur in minute crystals of ferberite and scheelite. Due to their close association with submarine volcanics and marine sediments, these pyritic copper deposits and the tungsten-bearing hematite beds are considered to be formed by submarine exhalant-sedimentary processes. During the yanshanian period there have been some weak reconstitution and superimposition by hydrothermal processes.