摘要
辽东地区古元古代辽河群火山-沉积建造中发育有大规模的菱镁矿矿床和硼酸盐矿床,是中国非金属矿产镁、硼的主产地.文章对这两类非金属矿床进行了主微量元素、稳定同位素（硫和碳）和LA-MC-ICP-MS锆石U-Pb定年测试.同时,结合部分前人的同位素测试结果对成矿作用进行了探讨,研究表明：①菱镁矿矿石及内部的石膏岩的δ^34 SV-CDT为15.6‰-26.5‰,硼矿石及其周缘硬石膏和大理岩围岩的δ^34 SV-CDT值和δ11B值分别为11.6‰-24.3‰和8.8‰-13.9‰,显示为海相蒸发沉积的特征;②菱镁矿矿体内黄铁矿δ^34 SV-CDT值为16.0‰-20.7‰,硼酸盐矿体内黄铁矿δ^34SV-CDT值为12.3‰-13.2‰,显示海相硫酸盐热还原成因的特征;③菱镁矿矿石的δ13CV-PDB值为0.3‰-1.6‰,硼酸盐矿床周缘新鲜大理岩围岩的δ^13CV-PDB值为-1.5‰-4.6‰,记录有受古元古代Lomagundi海相蒸发事件影响的碳同位素“正异常”现象;④菱镁矿矿石和硼矿体周缘的镁质大理岩均具有相似的页岩标准化稀土元素配分图和较高的硼含量;⑤菱镁矿和硼矿矿体上、下盘中的各类变粒岩和浅粒岩的岩浆锆石阴极发光图像相似,均具有的2.2Ga左右的峰期岩浆锆石年龄.因此,辽吉裂谷北缘斜坡区的菱镁矿矿床和中央凹陷区的硼酸盐矿床可能均形成于2.2Ga左右的海相蒸发沉积环境,形成于大规模火山喷发沉积活动的间歇期,属裂谷内南北两侧同期异相海相蒸发沉积的产物.
A large number of Paleoproterozoic magnesite and borate deposits hosted in the strata of volcanic-sedimentary sequence of Liaohe Group in eastern Liaoning province serve as significant sources of magnesium and boron in China. An integrated major and rare earth element, stable isotope （C and S） and LA-MC-ICP-MS zircon U-Pb dating study was carried out for these two types of nonmetallic ore deposits in combination with other data available. The results show that： ① the values of δ^34SV-CDT of marbles and ores in magnesite deposits range from 15.6‰ to 26.5‰, while the values of δ^34SV-CDT and δ11B of marbles and ores in borate deposits range from 11.6‰ to 24.3‰, and from 8.8‰ to 13.9‰, respectively, suggesting a marine evaporation genesis. ② the values of δ^34SV-CDT of pyrites in magnesite and borate deposits range from 16.0‰ to 20.7‰ and from 12.3‰ to 13.2‰, respectively, implying a marine evaporate reductive genesis; ③ the values of δ^13CV-PDB of magnesite range from 0.6‰ to 1.3‰, while values of relatively fresh marbles in borate deposits range from -1.5‰ to 4.6‰, which records marine evaporation related positive δ^13CV-PDB excursion of Lomagundi event; ④ the B content and PAAS-normalized REE patterns of magnesite and borate deposits are similar; and ⑤ the CL images and U-Pb results of zircons in leptynite and leptite located outside the magnesite and borate deposit are similar, with a peak magmatic peak age of 2.2 Ga. Therefore, the magnesite deposits and the borate deposits, which are located on the northern slope and in central depression, respectively, are synchrono-heteropic facies of evaporative mineralization formed in a rhythmic environment of evaporation and volcanic-sedimentation at about 2.2 Ga.
出处
《矿床地质》
CAS
CSCD
北大核心
2015年第3期547-564,共18页
Mineral Deposits
基金
国土资源部公益性行业科研专项经费项目(编号:201211074-2
200911043-20)资助
