闪锌矿中锗的沉淀机制研究——以会泽铅锌矿为例

As one of the most important dispersed elements, Ge occurs chiefly in Zn sulphide ores and coals. But this element in many of them is still not be utilized. The previous research on the geochemical behavior of Ge focus on the organophile in coals, but the sulfophile behavior is rarely be involved in most projects. So, why Ge can deposit with sphalerite? And how? To answer this question, this project focus on the precipitation mechanism of Ge element in Huize Pb-Zn deposit. From the mineral characteristic of sphalerite, there are two relationship need to be cut to the clarify: one is the relation between the crystal structure and the Ge element content of sphalerite, the other is the crystallization process and the change of fluid properties. Beginning with the careful observation, the mineralization stages of sphalerite is distinguished. The occurrence mechanism of Ge atom is revealed through the observation of crystal structure and analysis of in-situ of Ge content by Scanning Probe Microscope (SPM), microscale X Ray Fluorescence (μ-XRF) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The precipitation mechanism of Ge is established through the testing of T, P, component, pH etc of ore-forming fluids in different type of sphalerite, by temperature measured instrument, Laser Raman Microprobe, gas chromatography and ion chromatography. According to the research on ore-forming process and enrichment regularity of Ge in lead-zinc metallogenic hydrothermal, setting up the relationship between germanium and lead-zinc mineralization. Project will be to improve the understanding of Ge geochemical behavior in hydrothermal system, and to promote the level of comprehensive utilization for Ge, and helpful for the prospect to Ge ore deposits exploration.

作为一种重要的分散元素，锗广泛产于低温铅锌矿床的闪锌矿中，但多数铅锌矿区尚未被利用，其原因在于对锗在热液体系的“亲硫性”地球化学行为研究薄弱，尤其是在铅锌矿中锗为何能与闪锌矿一起沉淀成矿方面研究有待加强。项目以锗的沉淀机制研究为目标，从会泽铅锌矿床闪锌矿的矿物特征分析入手，查明（1）闪锌矿晶体结构与锗的富集规律，（2）富锗闪锌矿流体性质变化与沉淀机制。其方法是在精细划分闪锌矿形成阶段基础上，利用SPM、μ-XRF和LA-ICP-MS等，开展闪锌矿晶体结构观察和微区组分分析，查明锗元素在闪锌矿中的富集机制；利用冷热台、激光拉曼、气相和离子色谱等，开展不同类型、不同结构闪锌矿流体T、P、组分、pH等分析，查明富锗闪锌矿的沉淀机制，最终构建锗与铅锌成矿关系模式。项目有助于完善会泽铅锌矿床的成矿机制，提升对锗在硫化物矿床中地球化学行为的认知，指导川滇黔地区锗元素的综合利用，助推找矿勘查。

项目通过野外和镜下矿石矿物和脉石矿物共生组合、穿插关系观察，开展了锗与闪锌矿生成顺序关系研究，将会泽铅锌矿床中闪锌矿划分为3个世代。通过闪锌矿电子探针、ICP-MS、LA-ICP-MS、FE-SEM、μ-XRF和MAPPING开展形貌特征和微量元素含量分析，查明了会泽铅锌矿中富锗矿物为闪锌矿，其中第三世代中锗最为富集，次为第一世代，第二世代最低；闪锌矿晶体结构为六四面体，晶体内部颜色环带发育，其致色元素主要为铁元素；锗元素在其中的赋存形式主体为类质同象，元素替代机制主要为2Cu++Ge4+↔3Zn2+。通过流体包裹体温压、气液相组分分析，获得从第一世代到第三世代，闪锌矿成矿流体经历了中-中高温－中高盐度→中-中低温－中盐度→中低温－中低盐度的演化，明确锗的富集不完全受温度的控制，早世代锗元素富集受锗的高浓度控制，晚世代锗富集受温度控制；成矿流体化学条件显示Eh值逐渐增大，由弱还原性逐渐变为弱氧化性，pH值有逐渐变小，均处于酸性状态，pH值、Eh值通过控制流体中锗氢化物、锗合金氢化物活度影响锗元素富集。在锗在闪锌矿中富集规律和流体物理化学条件变化的基础上，建立了会泽铅锌矿锗的富集沉淀机制：早期富锗含矿热卤水与还原流体混合，在高盐度和低pH值、Eh值条件下形成锗相对富集的闪锌矿，其后随着流体中锗氢化物含量降低，形成锗含量较低的闪锌矿，再后随着流体温度降低，形成了锗最为富集的闪锌矿；最终在会泽铅锌矿沉淀成矿过程中，形成了闪锌矿中锗元素先富集后贫化再富集的沉淀富集演化规律。