摘要
上庄磷稀土(铁钪)矿床发育于南祁连拉脊山蛇绿混杂带中,该矿床的形成与地幔岩熔融分异活动密切相关,矿石矿物与其寄主岩石矿物一致,指示成岩成矿的同一性,但对其成矿是否为单一岩浆成因或有热液流体参与仍缺乏研究。利用电子探针(EPMA)和激光等离子质谱仪LA-ICP-MS原位分析技术,从黑云母、磁铁矿和磷灰石的矿物学特征角度讨论含矿磷灰黑云单斜辉石岩的成因。结果表明:磷灰黑云单斜辉石岩中磁铁矿和磷灰石形成要早于黑云母,黑云母呈明显褐色—褐黄色多色性,高Al、K、Ti,中等偏低Fe(X_(Fe)值为0.42~0.46)、Mg(X_(Mg)值为0.54~0.58),贫Ca和Na,属岩浆黑云母;磁铁矿V、Cr含量总体上较高,Mg含量低,Ni/Cr值不高于1(1个点除外),具有岩浆型磁铁矿的高V、Cr、Ti(部分较低)特征,且磁铁矿可能为早期结晶矿物;磷灰石为结晶程度较好的氟磷灰石,背散射图像中未发现热液型磷灰石或被热液溶蚀交代磷灰石具有的孔洞、裂隙、浑浊发暗等现象,其高F、贫Cl、低Cl/F值,高稀土元素总含量((2722~7730)×10^(-6)),轻、重稀土元素分馏明显,指示其为典型岩浆型磷灰石。综上所述,上庄磷稀土(铁钪)矿床为岩浆成因,成岩成矿可能与地幔岩部分熔融分异有关,在高温和氧化环境下,富磷、富挥发份F及少量含CO_(2)的流体为控制P、REE和Fe等成矿元素富集矿化的重要地球化学因素。
The Shangzhuang P-REE(-Fe-Sc)deposit is located in the ophiolitic melange zone in Lajishan area of South Qilian.The formation of the deposit is closely related to the melting and differentiation of mantle rocks,and the ore minerals are consistent with their host rock minerals,indicating the identity of diagenesis and mineralization,but there are still different understandings about whether the mineralization is caused by a single magma or hydrothermal fluid.Based on the mineralogical characteristics of biotite,magnetite and apatite,the genesis of ore-bearing apatite biotite clinopyroxenite was discussed by means of electron probe microanalysis(EPMA)and laser plasma mass spectrometer LA-ICP-MS in-situ analysis.The results show that the formation of magnetite and apatite from apatite biotite clinopyroxenite is earlier than that of biotite.Biotite is obviously brown polychrome,high in Al,K and Ti,moderately low in Fe(X Fe is 0.42-0.46),Mg(X Mg is 0.54-0.58),and poor in Ca and Na,indicating that it is of magmatic biotite;magnetite is generally high in V and Cr,low in Mg,and Ni/Cr ratio less than or equal to 1(except for one point),which is characterized by high V,Cr and Ti(partly low)of magmatic magnetite,and the magnetite may be an early crystalline mineral;apatite is fluorapatite with good crystallization degree,and BSE image does not find the holes,fissures,turbidity and darkness of hydrothermal apatite or metasomatized apatite by hydrothermal dissolution.It is high in F,poor in Cl,low in Cl/F ratio,high in total contents of rare earth elements((2722-7730)×10-6),and has obvious fractionation of light and heavy rare earth elements,indicating that it is typical magmatic apatite.Comprehensive study shows that Shangzhuang P-REE(-Fe-Sc)deposit is of magmatic genesis,and its diagenesis and mineralization may be related to partial melting and fractionation of mantle rocks.Under high temperature and oxidizing environment,the fluid rich in P,volatile F and a small amount of CO 2-bearing,is an important geochemical factor controlling the enrichment and mineralization of ore-forming elements such as P,REE and Fe.
作者
王进寿
陈鑫
朱丹
薛万文
金婷婷
王树林
WANG Jin-shou;CHEN Xin;ZHU Dan;XUE Wan-wen;JIN Ting-ting;WANG Shu-lin(Key Laboratory of Geological Process and Mineral Resources of Northern Qinghai Tibetan Plateau,Qinghai Geological Survey Institute,Xining 810012,Qinghai,China;School of Earth Resources,China University of Geosciences,Wuhan 430074,Hubei,China;Key Laboratory of Rare Earth and Scattered Minerals,Ministry of Natural Resources,Wuhan 430034,Hubei,China)
出处
《地球科学与环境学报》
CAS
北大核心
2023年第5期1094-1109,共16页
Journal of Earth Sciences and Environment
基金
青海省科学技术厅应用基础研究项目(2021-ZJ-741)。
