扬子地块北部早前寒武纪铁建造的特征、成因类型和构造背景

Early Precambrian Banded iron formations (BIFs), developed in many Archean cratons, provide the most important iron resources for human industry and “geologic barcodes” for the global correlation of Precambrian sedimentary records. BIFs are important repositories of the early Earth’s major environmental transitions, biological innovations and iron resources. Although a number of Neoproterozoic iron formations occur around the southeastern margin of the Yangtze block, so far there has been few report on Archean-Paleoproterozoic BIFs from this craton, which is in sharp contrast with the North China Craton to the north where Archean-Paleoproterozoic BIFs are abundant. Our recent studies on the Yingshan iron deposit at the northeastern margin of the Yangtze block indicated that the deposit was sentiment primary at about 2.45 Ga, display typical fabric and geochemical features of BIFs. Hence, several previous-called “magnetite quartzites” in several early Precambrian basement of the Yangtze block should have some genetic relationship and distribution rules. .This project will focus on three magnetite quartzite type iron deposit, such as the Yingshan iron deposit in Feidong Group of the Zhangbaling metamorphic belt, the Dianzihe iron deposit in Shuiyeshi Group of the Kongling complex, and the Huangjiaying iron deposit in North Yangtze block. Based on comparative studies on wall-rock sedimentary formations, formation ages, depositional environments of these iron formations, temporal and spatial distribute characters of these early Precambrian BIFs will be revealed in detail. Our contribution will provide important implications to reconstruction of early Precambrian evolution of the Yangtze block, and helpful information for evaluation of early Precambrian Iron ore resources of south China.

早前寒武纪条带状铁建造(BIF)在众多克拉通广泛发育，是全球最重要的铁矿资源，也是地球早期历史和克拉通早期演化的重要记录，对于理解古老陆壳演化具有重大价值。中国的晚太古-早元古代BIF主要发育于华北克拉通，扬子地块由于古老基底出露局限，早前寒武纪BIF鲜有报导。申请人的前期工作发现，产于肥东群的英山铁矿沉积时代为~2.45Ga，具有BIF的典型组构和地球化学特征，且属于扬子地块的一部分，因而扬子北部早前寒武系变质基底中所发育的磁铁石英岩很可能有一定的成因联系和分布规律。.本项目拟对赋存于张八岭变质带肥东群、崆岭杂岩水月寺群和碧口地体鱼洞子群的英山铁矿、店子河铁矿和黄家营铁矿床开展围岩建造、沉积时代、沉积环境和构造背景等方面的对比研究，在确认其是否为BIF的基础上，揭示扬子地块早前寒武铁建造的发育特征，探讨克拉通早期演化与BIF的成因联系，为华南早前寒武铁矿资源的评价提供理论依据。

早前寒武纪条带状铁建造(BIF)是全球最主要的铁资源，记录了早期地球环境演化的重要信息。中国的太古宙—古元古代BIF主要发育于华北克拉通，扬子克拉通由于古老基底出露局限，因而早前寒武纪BIF鲜有报导。本项目识别出扬子地块北缘古老基底中存在BIF型铁矿并对其进行了深入研究，取得如下成果和认识。(1) 张八岭变质带肥东群中英山铁矿沉积时代为~2.45 Ga；崆岭杂岩中店子河铁矿沉积时代为2.88‒2.80 Ga；鱼洞子杂岩中龙王沟铁矿沉积于~2.45 Ga，黑山沟铁矿沉积于~2.75 Ga。(2) 英山、龙王沟和黑山沟铁矿围岩的原岩均为碎屑岩和火山岩，属阿尔戈马型BIF。店子河铁矿围岩的原岩主体为变泥质岩，属苏必利尔型BIF。上述BIF型铁矿普遍经历ca. 2.0‒1.8 Ga的变质，变质程度达角闪岩—麻粒岩相。(3) 英山、黑山沟、龙王沟铁矿沉积于相对还原的深水环境中，成矿物质来源为海底高温热液混合海水；不产氧光合作用微生物可能驱动二价铁氧化为铁氢氧化物进而成矿。黑山沟铁矿可能形成于弧后盆地中。店子河铁矿沉积于氧化的浅水环境，由产氧光合作用驱动铁-锰氢氧化物沉淀进而成矿。(4) 英山铁矿共生矿物间达到了Fe-O同位素平衡，指示其曾经历一个快速的抬升剥露过程，可能响应三叠纪扬子—华北碰撞造山事件。本项目的实施为进一步的扬子地块早前寒武纪BIF型铁矿基础科学研究和找矿勘查奠定基础。项目期间培养博士生2名，硕士生2名，发表国际论文8篇，核心国内论文1篇。