报告题目：磁铁矿Fe-Zn同位素组成制约大型IOA和矽卡岩型铁矿床成因

报告地点：伟德BETVLCTOR1946始于英国纬地楼3楼会议室

报告时间：2019年1月4日（星期五）下午4:00-5:30

报告人：贺治伟博士

报告人简介：

 贺治伟，湖北孝感人，博士生。2008年-2012年就读中国地质大学（武汉），资源勘查工程（工科基地班）专业，2012年-至今中国科学技术大学地球化学专业硕博连读，导师黄方教授，研究方向包括单斜辉石与熔体分配系数研究、岩浆-热液矿床Fe-Cu-Zn等金属同位素研究。2016年9月至2018年9月在苏黎世联邦理工学院进行博士生联合培养，导师Derek Vance教授，研究方向为现代海洋洋底沉积物和孔隙水的金属稳定同位素研究，包括Fe-Zn-Ni-Mo-U等同位素体系。目前从事研究领域主要为金属同位素在高温岩浆-热液矿床和低温表生过程中的应用。

报告内容简介：

  IOA型铁氧化物矿床是地球重要铁矿资源之一，但是它们的成因至今存在争议。本报告将报道来自瑞典北部Kiruna IOA铁矿，大冶地区矽卡岩铁矿，以及斑岩铜矿的磁铁矿Fe-Zn同位素组成。通过系统对比来自这些典型岩浆-热液矿床的磁铁矿Fe-Zn同位素组成差异，我们对IOA矿床的成因提供了新的认识。

ABSTRACT

 Kiruna-type iron oxide deposits are an important iron source on Earth, yet their origin remains controversial. Here we provide new insight into Kiruna-type iron oxide ore genesis by determining iron and zinc isotopic compositions of magnetite from the well-described Kiruna iron deposits in Sweden, Daye skarn iron deposit in China, and two porphyry Cu deposits (PCDs). We found high variability in both d⁵⁶Fe and d⁶⁶Zn values for magnetite from different ore systems. Magnetite from the Kiruna iron deposits has d⁵⁶Fe between 0.10‰ and 0.26‰, with a mean value of 0.14‰, which is essentially unfractionated from the mantle-derived silicate magmas. While the d⁶⁶Zn (0.35‰ and 0.50‰) is positively shifted from the magma source. These values are interpreted as reflecting a primary high-temperature igneous origin for the Fe-oxides. Instead, magnetite from the PCDs show high-d⁵⁶Fe and low-d⁶⁶Zn signatures, reflecting a single hydrothermal origin. The d⁵⁶Fe and d⁶⁶Zn of magnetite from the Daye skarn iron deposit are almost intermediate between those of magnetite from the Kiruna iron deposits and PCDs, reflecting an interplay between magmatic and hydrothermal processes related to the Fe-oxide formation. We propose that the essential differences of the ore genesis among Kiruna-type iron deposits, skarn iron deposits, and the PCDs are their primary volatile contents and ore-forming temperatures. We highlighted that Kiruna-type iron deposits are essentially formed at higher temperatures with less volatile contents than the porphyry and skarn deposits. These findings challenge previous hypotheses of iron- and silica-rich liquid immiscibility as the primary mechanism for the formation of the Kiruna-type iron oxide deposits.

（信息来源：汪方跃）