四川省同德石墨矿床地球化学特征及Re-Os同位素定年

Geochemical Characteristics and Re-Os isotopic dating of Tongde Graphite Deposit, Sichuan Province

攀枝花同德石墨矿床位于扬子板块西缘增生带,本文对矿区矿石和赋矿围岩进行全岩地球化学分析、对矿石进行碳同位素测定、Re-Os同位素测年、对矿石及其赋矿岩石进行了原岩恢复并探讨了成矿环境。研究表明,矿石SiO_(2)为55.65%~61.68%,SiO_(2)/Al_(2)O_(3)比值为4.59~5.42,Ni/Co比值6.23~12.88,富集Ba、Rb、Sr等大离子亲石元素和Nb、Zr、Hf、Th、U等高场强元素。矿石的稀土元素总量ΣREE为149.13×10^(-6)~195.37×10^(-6),具有弱的Ce负异常和Eu负异常,代表了缺氧的海相沉积环境。矿石中δ^(13)CV-PDB值为-25.0‰~-23.5‰,位于生物成因的有机碳范围内,表明其成矿碳质主要来源于有机物。石墨的Re-Os同位素年龄为983±72 Ma(MSWD=1.7),时代归属为新元古代早期,早于同德周边岩浆岩侵入时代。Re的含量介于27.66×10^(-9)~79.81×10^(-9),普通Os和^(187)Os的含量分别为0.52×10^(-9)~2.16×10^(-9)、0.28×10^(-9)~0.83×10^(-9),相对于Re、Os在地壳中的丰度显著富集。^(187)Re/^(188)Os比值为122.9~350.5,Os同位素初始比值^(187)Os/^(188)Os=0.31±0.21。结合野外地质调查对同德地区矿石和赋矿云母石英片岩进行原岩恢复,得出其原岩为沉积岩。

The Tongde Graphite Deposit in Panzhihua is located in the accretionary zone on the western margin of the Yangtze plate. In this paper, the whole rock geochemical analysis, C isotope determination and Re-Os isotope dating of the ore in Tongde graphite mining area are carried out, the original rock of the ore is restored, and the metallogenic environment is discussed. Research shows that the ore SiO_(2)is 55.65~61.68%, SiO_(2)/Al_(2)O_(3) ratio is 4.59~5.42, and Ni/Co ratio is 6.23~12.88. It is rich in Ba, Rb, Sr and other large ion lithophile elements and Nb, Zr, Hf, Th, U and other high field strength elements. Total rare earth elements of ore ΣREE is 149.13×10^(-6)~ 195.37×10^(-6), with weak Ce negative anomaly and Eu negative anomaly, representing the anoxic marine sedimentary environment. The Carbon isotope δ^(13)CV-PDBin ore is-25.0‰~-23.5‰, which is within the range of biogenic organic carbon, indicating that the ore-forming carbon mainly comes from organic matter. The Re-Os isotopic age of graphite is 983 ± 72 Ma(MSWD=1.7),belonging to the early Neoproterozoic, earlier than the intrusion age of magmatic rocks around Tongde. The content of re is between 27.66×10^(-9)~79.81×10^(-9), the contents of ordinary Os and 187Os are 0.52 ×10^(-9)~2.16×10^(-9), 0.28 × 10^(-9)~0.83×10^(-9),respectively,it is significantly enriched relative to the abundance of Re and Os in the crust. The ^(187)re/^(188)os ratio is 122.9~ 350.5, and the initial Os isotope ratio ^(187)Os/^(188)Os=0.31±0.21. Combined with the field geological survey, the original rock of ore and ore bearing mica quartz schist in Tongde area is restored, and it is concluded that the original rock is sedimentary rock.