Geological implications of apatite within the granite-related Jiepai W-(Cu) deposit, Guangxi, South China
Geological implications of apatite within the granite-related Jiepai W-(Cu) deposit, Guangxi, South China
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广西界牌钨（铜）矿床中磷灰石的地质意义
DOI：
10.1016/j.oregeorev.2021.104548
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发表时间：
2021
影响因子：
3.3
通讯作者：
Lin Shuping
中科院分区：
文献类型：
--
作者：
Zhang Jian;Huang Wenting;Wu Jing;Liang Huaying;Lin Shuping
界牌钨（铜）存款是华南苗儿山-越城岭岩体中与加里东期花岗岩有关的最大钨矿床之一。该存款由矽卡岩型和蚀变花岗岩型矿化沿着组成，并有一个以蚀变长石砂岩为容矿岩的矿体。这项研究提出了新的岩相学和地球化学数据磷灰石新鲜的黑云母花岗岩（API），矿化黑云母花岗岩（ApII）和矿笋（ApIII）样品，并使用这些数据来约束岩浆和热液过程，形成的存款。API与原生黑云母有关，在背散射电子（BSE）成像过程中可见核-环纹理或振荡分区，表明这种磷灰石具有岩浆起源。ApII与白钨矿和次生黑云母有关，由具有振荡环带的BSE亮核（ApIIa）和不含流体包裹体的BSE暗边（ApIIb）包围的罕见流体包裹体组成。这些关系表明，ApIIa和ApIIb记录的影响，轻微和显著的流体交代作用，分别。在BSE成像过程中，ApIII似乎是均匀的，与丰富的白钨矿，绢云母和石英有关，并含有丰富的流体包裹体，表明热液起源。API的稀土元素总量（2959-14057 ppm）和Y（1598-9099 ppm）含量从核到边缘逐渐增加，Na_2 O（0.05- 0.2wt%）和MnO（0.1- 0.32wt%）含量高，Sr（71.6- 86.1ppm）含量低，LaN/YbN值（0.55-1.21）低。ApIIa的稀土元素和钇含量与API相近，但Sr含量较高（194-258 ppm），Na_2 O含量较低（<0.03wt%），MnO含量较低（0.04- 0.11wt%）。ApIIb的Na_2 O、MnO和Sr含量与ApIIa相似，但稀土（1766-2021 ppm）和钇（1128-1512 ppm）含量较低。ApIII磷灰石的Na_2 O、MnO、REE和Y含量与ApIIb相似，但Sr含量略低（103-173 ppm），LaN/YbN值较高（0.92-3.28），API内REE含量从核部到边缘的大幅度增加表明其结晶时间延长，产生富W的残余熔体，最终形成W矿化。ApIIa和ApIIb含有与ApIII相似的Na、Mn和Sr含量，但具有分别与API和ApIII相似的REE含量。这表明Na、Mn和Sr受到弱流体交代作用的影响，而REE只能通过显著的流体交代作用被活化。ApIII相对较低的REE含量和较高的LaN/YbN值反映了大量白钨矿的存在。这些数据表明，API，ApII和ApIII都具有不同的结构和地球化学（Na，Mn，Sr，Y，REE和LaN/YbN）特征和流体包裹体种群。磷灰石是与花岗岩有关的钨（铜）成矿的潜在找矿指示矿物。
The Jiepai W–(Cu) deposit is one of the largest Caledonian granite-related W deposits in the Miaoershan–Yuechengling (MY) pluton of southern China. The deposit consists of skarn-type and altered granite-type mineralization along with an ore shoot hosted by altered arkose. This study presents new petrographic and geochemical data for apatite from fresh biotite granite (ApI), mineralized biotite granite (ApII), and ore shoot (ApIII) samples and uses these data to constrain the magmatic and hydrothermal processes that formed the deposit. ApI is associated with primary biotite and has core–rim textures or oscillatory zoning visible during backscattered electron (BSE) imaging, indicating that this apatite has a magmatic origin. ApII is associated with scheelite and secondary biotite and consists of BSE-bright cores (ApIIa) with oscillatory zoning and rare fluid inclusions surrounded by BSE-dark rims (ApIIb) free of fluid inclusions. These relationships suggest that ApIIa and ApIIb record the effects of slight and significant fluid metasomatism, respectively. ApIII appears homogenous during BSE imaging, is associated with abundant scheelite, sericite and quartz, and contains abundant fluid inclusions, indicative of a hydrothermal origin. ApI has increasing total rare earth elements (REE) (2959–14057 ppm) and Y (1598–9099 ppm) contents from cores to rims, high Na2O (0.05–0.2 wt%) and MnO (0.1–0.32 wt%) and low Sr (71.6–86.1 ppm) contents, and low LaN/YbNvalues (0.55–1.21). ApIIa contains similar REE and Y contents to ApI, but has higher Sr (194–258 ppm) and lower Na2O (<0.03 wt%) and MnO (0.04–0.11 wt%) contents. ApIIb contains similar Na2O, MnO, and Sr contents to ApIIa, but with much lower REE (1766–2021 ppm) and Y (1128–1512 ppm) contents. ApIII apatite has similar Na2O, MnO, REE, and Y contents to ApIIb, but with slightly lower Sr (103–173 ppm) contents and higher LaN/YbNvalues (0.92–3.28).The large increase in REE contents from core to rim within ApI is indicative of prolonged crystallization, generating W-enriched residual melts and eventually W mineralization. ApIIa and ApIIb contain similar Na, Mn, and Sr contents to ApIII, but have REE contents that are similar to ApI and ApIII, respectively. This suggests that Na, Mn, and Sr were affected by weak fluid metasomatism, whereas REE can only be mobilized by significant fluid metasomatism. The relatively low REE contents and high LaN/YbNvalues of ApIII reflect the presence of abundant co-precipitated scheelite. These data indicate that ApI, ApII, and ApIII all have different textural and geochemical (Na, Mn, Sr, Y, REE, and LaN/YbN) characteristics and fluid inclusion populations. All of this suggests that apatite is a potential indicator mineral in mineral exploration for granite-related W–(Cu) mineralization.