Mineralization processes in the Bainaimiao Cu-Au deposit in Inner Mongolia, China: Constraints from geology, geochronology, and mineralogy

IF 3.2 2区 地球科学 Q1 GEOLOGY Ore Geology Reviews Pub Date : 2024-10-11 DOI:10.1016/j.oregeorev.2024.106276
Changhao Li , Ping Shen , Branimir Šegvić , Pei Li , Chong Cao , Ge Ma , Qingyu Suo , Haoxuan Feng , Xiangkai Chu
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Abstract

The Central Asian Orogenic Belt underwent complex tectonic processes and is one of the most intensely accretionary areas globally. Porphyry copper deposits within the belt were likely subjected to deformation during tectonic processes. The Bainaimiao Cu-Au deposit is a typical example of a deformed porphyry deposit whose formation processes include a porphyry emplacement (Event I), a greenschist facies metamorphism (Event II), and a brittle deformation (Event III). Geochronology and trace element geochemistry of zircon, volatiles of magmatic apatite, along with the assemblages, textures, abundances, and compositions of phyllosilicates from these three events were investigated to unveil the physicochemical conditions under which the key geological events relevant to the deposit formation took place. LA-ICP-MS zircon U-Pb dating shows that the granodiorite porphyry in the northern and southern zones formed at 447.4 ± 1.6 to 445.8 ± 3.6 Ma and 436.1 ± 3.8 to 434.1 ± 3.3 Ma, respectively. The granodiorite porphyry in the northern zone has higher oxygen fugacity and Clmelt content but similar Smelt and Fmelt contents compared to the granodiorite porphyry in the southern zone. Microscopic and mineralogic observations point to Event I to be of high plagioclase (22–67 vol%) and quartz (6–40 vol%) content with a range of hydrothermal minerals related to potassic, phyllic, and propylitic alterations. Event II features high amphibole (38–83 vol%) or epidote-chlorite (up to 77 vol%) content with minerals precipitating along the schistosity planes. Event III is characterized by wide veins (3–80 cm) and the highest quartz (61–65 vol%) and calcite (12–19 vol%) content. Geothermometry results show the temperature of potassic and phyllic alterations of Event I to be ∼622 °C and ∼288 °C, respectively. Based on geothermometry and P-T pseudosections, the temperatures of metamorphism and metallic precipitation of Event II were ∼271–634 °C and 297–328 °C, respectively. Both mechanical and chemical mobilization of metallic elements results in Cu mineralization during Event II. The metallic precipitation temperatures of Event III spanned from 297 to 328 °C according to chlorite geothermometry. The ratios of Fe3+/Fetotal and Mg/(Mg + Fetotal) of biotite, chlorite Fe/(Fe + Mg), and white K-mica composition show the mineralizing fluid of Event III to be the most oxidized while that of Event II is the most reduced, F-rich and features the lowest water/rock ratio. This study suggests that deformation processes can increase the Cu mineralization grade of the deformed porphyry deposits through mobilization and re-precipitation of metallic elements.

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中国内蒙古白乃庙铜金矿的成矿过程:地质学、地质年代学和矿物学的制约因素
中亚造山带经历了复杂的构造过程,是全球增生最强烈的地区之一。带内的斑岩铜矿床很可能在构造过程中发生了变形。白乃庙铜金矿床是典型的变形斑岩矿床,其形成过程包括斑岩喷出(事件 I)、绿泥石面变质(事件 II)和脆性变形(事件 III)。对这三个事件中的锆石、岩浆磷灰石挥发物以及植硅体的组合、质地、丰度和成分进行了地质年代学和微量元素地球化学研究,以揭示与矿床形成相关的关键地质事件发生的物理化学条件。LA-ICP-MS 锆石 U-Pb 定年显示,北部和南部区域的花岗闪长斑岩分别形成于 447.4 ± 1.6 至 445.8 ± 3.6 Ma 和 436.1 ± 3.8 至 434.1 ± 3.3 Ma。与南区花岗斑岩相比,北区花岗斑岩的氧富集度和Clmelt含量较高,但Smelt和Fmelt含量相近。显微镜和矿物学观察表明,事件 I 的斜长石(22-67 vol%)和石英(6-40 vol%)含量较高,并伴有一系列与钾盐化、植酸化和丙酸化有关的热液矿物。事件 II 的特点是闪石(38-83 vol%)或绿泥石(高达 77 vol%)含量高,矿物沿片岩平面沉淀。事件 III 的特点是矿脉较宽(3-80 厘米),石英(61-65 Vol%)和方解石(12-19 Vol%)含量最高。地温测量结果显示,事件 I 的钾盐化和植物化温度分别为 ∼622 °C和 ∼288 °C。根据地热测定法和P-T伪剖面,事件II的变质和金属沉淀温度分别为 ∼271-634 °C和297-328 °C。在事件 II 期间,金属元素的机械和化学移动都导致了铜矿化。根据绿泥石地热测定法,事件 III 的金属沉淀温度介于 297 ℃ 至 328 ℃ 之间。生物岩的Fe3+/Fetotal和Mg/(Mg + Fetotal)比值、绿泥石的Fe/(Fe + Mg)比值以及白K云母成分表明,事件III的成矿流体氧化程度最高,而事件II的成矿流体还原程度最高,富含F,水/岩石比值最低。这项研究表明,变形过程可以通过金属元素的移动和再沉淀提高变形斑岩矿床的铜矿化品位。
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来源期刊
Ore Geology Reviews
Ore Geology Reviews 地学-地质学
CiteScore
6.50
自引率
27.30%
发文量
546
审稿时长
22.9 weeks
期刊介绍: Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers.
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