昆明理工大学任涛团队的一项最新研究，报道了滇西北普朗巨型斑岩型铜—多金属矿床岩浆生成减少及其意义。相关论文于2024年4月1日发表在《地球化学学报》上。

据悉，普朗巨型斑岩型铜-钼多金属矿床位于三江特提斯构造区域的中心——中甸地区，是由中闸地块下的甘孜—理塘洋板向西俯冲形成的。黄铜矿—磁黄铁矿—黄铁矿—辉钼矿以浸染状、脉状、细脉状和网状，分布在二长斑岩的钾硅酸盐蚀变带中，该蚀变带被青斑岩化叠加。电子探针显微分析(EPMA)对黑云母和角闪石的化学成分表明，成矿岩浆和出溶流体经历了氧逸度(fO₂)持续降低。

在岩浆阶段，原生角闪岩和黑云母(I型)在相对较高的温度(744-827℃)和低fO₂ (logfO₂=-12.26到-11.91)下结晶。与原始岩浆相比，岩浆中溶解的热液温度相对较低(621-711℃)，fO₂ (logfO₂ =-14.36到-13.32)。此外，矿石中磁黄铁矿含量高，原生磁铁矿和硫酸盐(即硬石膏和石膏)含量不足，表明该矿床可能为还原型斑岩矿床。结合前人对普朗矿床岩浆fO₂ 的研究和本研究中岩浆和流体fO₂ 结果，与普朗矿组合伴生的岩浆最初是一种高氧化岩浆，随后被图姆沟组的沉积岩还原。

附：英文原文

Title: Reduced magma generation and its implications for the Pulang giant porphyry Cu-polymetallic deposit in Northwest Yunnan, China

Author: Guan, Jingwei, Ren, Tao, Wang, Lei, Guan, Shenjin, Wu, Lianrong, Shi, Baosheng

Issue&Volume: 2024-04-01

Abstract: The Pulang giant porphyry Cu-Mo polymetallic deposit is located in the Zhongdian area in the center of the Sanjiang Tethys tectonic domain, which was formed by the westward subduction of the Garze-Litang oceanic slab beneath the Zhongza massif. Chalcopyrite-pyrrhotite-pyrite-molybdenite occurs as disseminations, veins, veinlets, and stockworks distributed in the K-silicate alteration zone in the monzonite porphyry, which is superimposed by propylitization. The chemical compositions of biotite and amphibole analyzed by electron probe microanalysis (EPMA) indicate that the ore-forming magma and exsolved fluids experienced a continuous decrease in the oxygen fugacity (fO₂). Primary amphibolite and biotite (type I) crystallized at relatively high temperatures (744–827 °C) and low fO₂ (logfO₂=-12.26 to -11.91) during the magmatic stage. Hydrothermal fluids exsolved from the magma have a relatively lower temperature (621–711 °C) and fO₂ (logfO₂=-14.36 to -13.32) than the original magma. In addition, the presence of a high abundance of pyrrhotite and an insufficiency of primary magnetite and sulfate in the ore (i.e., anhydrite and gypsum) indicate that the deposit may be a reduced porphyry deposit. Magma and fluid fO₂ results, combined with previous research on magmatic fO₂ at the Pulang deposit, indicate that the magma associated with the reduced Pulang ore assemblages was initially generated as a highly oxidized magma that was subsequently reduced by sedimentary rocks of the Tumugou Formation.

DOI: 10.1007/s11631-024-00686-2

Source: https://link.springer.com/article/10.1007/s11631-024-00686-2