摘要
扬子地台及邻区下寒武统黑色岩系底部是钡富集的重要层位,广泛分布的重晶石矿床主要赋存在暗色硅岩中。毒重石(BaCO_2)、钡解石[BaCa(CO_3)_2]矿床的分布仅限于大巴山断裂北侧,即陕南与川北地区。毒重石与钡解石、重晶石、磷结核、黑色硅岩、黑色页岩、钒矿和石煤等构成特有的沉积序列。毒重石的δ^(13)”C_(PDB)平均值为-16.4‰,反映了形成毒重石的碳为有机成因,钡主要来源于海底火山、热泉与生物。
Witherite ore deposits are located from Ziyang to Chengkou on the northern side of the Dabashan fault zone along the boundary between Shaanxi and Sichuan provinces.Witherite orebeds occur in black shale series which are composed of black chert,black shale and phosphorous concretion-bearing siliceous and arillaceous rocks.Barite,baritocalcite and vana- dium minerals are intergrown with the witherite.The ore-bearing series with Ba-Si-P-V-C-S- O element association is similar to that of the barite deposits located on the Yangtze platforna and in adjacent geosyncline.Witherite orebeds occur at the bottom of Lower Cambrian black shale series near the boundary between Sinian and Cambrian. Analytical results of carbon and oxygen isotopes in the witherite show that the mean values of δ^(13)C_(PDB) and δ^(18)O_(PDB)are-18‰ and-11‰ in Ziyang,-14‰ and-13‰ in Chengkou,respectively.Carbon isotopes in the witherite show the characteristics of sedimentary origin related to the biogenesis and diagenesis.This is also demonstrated by the measurement of higher organic carbon content in witherite orebeds,black shale and black chert. Origin of witherite is related to anoxic environment and diluted ore-forming solution. Since Late Sinian this area was gradually closed with the deepening sea.The decomposition of the abundant died organisms released barium to the seawater.Volcanic activity and hot spring provided a huge amount of barium.Witherite formed under reduction condition.
出处
《地质科学》
CAS
CSCD
北大核心
1992年第3期237-248,共12页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金(4860108)
关键词
寒武纪
黑色岩系
毒重石
矿床
成因
Cambrian black shale series
Witherite
Carbon isotope
Dabashan
