幕阜山矿集区黄柏山锂铌钽矿床地质特征及找矿方向

江南造山带中段幕阜山稀有金属矿集区是我国东部重要的锂铌钽资源基地, 区域锂资源主要集中于锂辉石伟晶岩中。但此类伟晶岩常受到岩浆出溶热液的叠加作用, 导致锂不同程度的流失, 因此新鲜锂辉石伟晶岩的产出条件与精准定位, 成为区域成矿理论研究与锂资源勘查的突破重点。笔者研究团队近年来在幕阜山地区新发现的黄柏山锂铌钽矿床, 产出了区域少有的大规模新鲜锂辉石伟晶岩脉。本次研究在黄柏山矿床已开展的化探、探槽、钻探等勘查工作基础上, 系统总结了矿床的地质条件, 精确厘定其成矿时代, 初步建立了仁里-黄柏山矿田成矿模型, 并进一步指出区域找矿方向。黄柏山矿床位于幕阜山岩体西南缘, 矿床内伟晶岩总体沿片岩片理产出, 其类型主要为(白云母)钠长石伟晶岩和锂辉石钠长石伟晶岩, 稀有金属矿化组合为Be-Nb-Ta-Li, 稀有金属矿物主要为绿柱石、铌钽铁矿和锂辉石。
矿床内锂辉石多为新鲜无蚀变(＞96%), 少数晶体边缘具弱蚀变或锂辉石+石英蠕虫状共生结构, 为岩浆演化晚阶段流体出溶导致的弱酸性交代所致。三种类型锂辉石的Li2O为7.72%~7.82%, 基本未发生锂的流失, 这与区域构造交汇导致容矿空间封闭性弱, 岩浆演化出溶热液第一时间运移扩散有关。黄柏山矿床稀有金属成矿作用发生在早白垩世(133.0±1.5Ma), 与幕阜山矿集区二云母花岗岩成矿阶段时限(135.8~133.0Ma)一致。本次工作通过对仁里-黄柏山矿田伟晶岩地表类型分带的重新厘定, 结合区域已有的成矿母岩及伟晶岩垂向分带研究成果, 提出黄柏山矿床、仁里矿床、深部成矿母岩三者从西至东呈现出由高至低的三维空间分布特征, 初步建立矿田"体中体"模型。该模型及稀有金属成矿作用特点显示, 矿田西南部冷家溪群与幕阜山岩体接触带区域, 尤其是高地形地区, 仍具有锂找矿潜力。

Geological characteristics and prospecting direction of Huangbaishan Li-Nb-Ta deposit in Mufushan ore concentration area

The Mufushan rare-metal ore concentration area in the middle of Jiangnan orogenic belt is an important Li-Nb-Ta resource base in eastern China. The regional lithium resources are mainly concentrated in spodumene pegmatites. However, these pegmatites are often subject to the alteration of magmatic exsolution hydrothermal solution, resulting in the loss of lithium to varying degrees. Therefore, the production conditions and precise positioning of fresh spodumene pegmatites have become the breakthrough focus of regional metallogenic theory research and lithium resource exploration. The Huangbaishan Li-Nb-Ta deposit newly discovered by authors' team in Mufushan area has a rare large-scale fresh spodumene pegmatite vein. This study revealed the metallogenic characteristics of the Huangbaishan pegmatite deposit, determined the precise metallogenic age, preliminarily established the metallogenic model of the Renli-Huangbaishan ore field, and analyzed the prospecting prospect of the region. The pegmatite types of Huangbaishan deposit are mainly (muscovite) albite pegmatite and spodumene albite pegmatite, which generally occur along the schistosity of schist. The rare metal mineralization association is Be-Nb-Ta-Li and the rare metal minerals are mainly beryl, niobium-tantalite and spodumene. Spodumenes in the deposit are most (> 96%) fresh ones, while a few crystal edges have weak alteration or spodumene+quartz worm-like symbiotic structures caused by weak acid metasomatism through fluid dissolution in the late stage of magmatic evolution. The Li2O of three types of spodumenes varied from 7.
72% to 7.82%, showing no loss of lithium as always caused by the diffusion of the hydrothermal of magma differentiation due to the regional tectonic intersection. The rare metal mineralization of the Huangbaishan deposit occurred in the Early Cretaceous (133.0±1.5Ma), which is consistent with the two-mica granite related mineralization epoch in the Mufushan ore concentration area (135.8~133.0Ma). By redefining the zoning of pegmatite type in Renli-Huangbaishan ore field, and combining with the existing research of vertical zoning and metallogenetic parent rock, it is proposed that the Huangbaishan and Renli deposits and their deep metallogenetic parent rocks present a three-dimensional spatial distribution feature from west to east and from high to low. Then, the "body in body" exploration model of the ore field was preliminarily established. The model and the characteristics of rare metal mineralization show that the contact zone between Lengjiaxi Group and the Mufushan complex in the southwest of the ore field, especially the high terrain area, still has lithium prospecting potential.