The Dulong Sn-Zn-In polymetallic deposit in the Yunnan province, SW China, hosts a reserve of 5.0 Mt Zn, 0.4 Mt Sn, and 7 Kt In. It is one of the most important polymetallic tin ore districts in China. Granites at Dulong mining area include mainly the Laojunshan granite (third phase), which occurs as quartz porphyry or granite porphyry dikes in the Southern edge of the Laojunshan intrusive complex. Granites of phases one and two are intersected at drill holes at depth. There are three types of cassiterite mineralization developed in the deposit: cassiterite-magnetite ± sulfide ore (Cst I), cassiterite-sulfide ore (Cst II) within the proximal skarn in contact with the concealed granite (granites of phases one to two and three), and cassiterite-quartz vein ore (Cst III) near porphyritic granite. Field geology and petrographic studies indicate that acid neutralising muscovitization and pyroxene reactions were part of mechanisms for Sn precipitation resulting from fluid-rock interaction. In situ U–Pb dating of cassiterite samples from the ore stages of cassiterite-sulfide (Cst II) and Cassiterite-quartz vein (Cst III) yielded Tera-Wasserburg U–Pb lower intercept ages of 88.5 ± 2.1 Ma and 82.1 ± 6.3 Ma, respectively. The two mineralization ages are consistent with the emplacement age of the Laojunshan granite (75.9–92.9 Ma) within error, suggesting a close temporal link between Sn-Zn(-In) mineralization and granitic magmatism. LA-ICPMS trace element study of cassiterite indicates that tetravalent elements (such as Zr, Hf, Ti, U, W) are incorporated in cassiterite by direct substitution, and the trivalent element (Fe) is replaced by coupled substitution. CL image shows that the fluorescence signal of Cst I–II is greater than that of Cst III, which is caused by differences in contents of activating luminescence elements (Al, Ti, W, etc.) and quenching luminescence element (Fe). Elevated W and Fe but lowered Zr, Hf, Nb, and Ta concentrations of the three type cassiterites from the Dulong Sn-Zn-In polymetallic deposit are distinctly different from those of cassiterites in VMS/SEDEX tin deposits, but similar to those from granite-related tin deposits. From cassiterite-magnetite ± sulfide (Cst I), cassiterite-sulfide ore (Cst II), to cassiterite-quartz vein ore-stage (Cst III), high field strength elements (HFSEs: Zr, Nb, Ta, Hf) decrease. This fact combined with cassiterite crystallization ages, indicates that Cst I–II mainly related to concealed granite (Laojunshan granites of phases one and two) while Cst III is mainly related to porphyritic granite (Laojunshan granites of phase three).

都龙锡锌铟多金属矿床位于滇东南老君山锌锡钨多金属矿集区，是我国超大型锡石硫化物矿床之一及第二大铟矿床。前人研究表明，该矿床中铟主要以类质同象形式赋存于闪锌矿、黄铜矿中，尚未在原位矿石中明确鉴定出铟的独立矿物。本文基于都龙矿区来龙矿段矿石样品，综合开展扫描电镜（SEM）、电子探针（EPMA，包括元素面扫描）、LA-ICP-MS及激光拉曼光谱等分析，对铟在寄主硫化物和独立矿物相中的赋存状态进行了系统研究。LA-ICP-MS分析结果显示，闪锌矿与黄铜矿是铟的主要寄主矿物；时间分辨率曲线进一步指示In主要以类质同象形式赋存在闪锌矿和黄铜矿晶格中。更为重要的是，本文在硫化物矿石中原位识别出铟的独立矿物——硫铟铜矿。该矿物产自斑杂-斑块状矽卡岩型硫化物矿石中，多为半自形-他形不规则粒状-短柱状，粒径一般为2~8μm，主要呈粒间型（Rq-Ⅰ）赋存于闪锌矿与黄铜矿间隙，少量呈粒内型（Rq-Ⅱ）分布于闪锌矿内。电子探针成分分析显示其主量元素含量为Cu（25.61%~27.32%）、In（35.00%~45.47%）、S（25.82%~27.76%），化学式范围为Cu_0.94-1.06In_0.70-0.99Fe_0-0.09Zn_0.01-0.13S_2.00，简化式接近硫铟铜矿标准化学式CuInS₂；电子探针元素面扫描分析显示其为成分均匀的富铟独立矿物相。经非对称最小二乘法基线扣除与Voigt峰形拟合解析，硫铟铜矿拉曼光谱主峰包络在200~400cm^-1区间内呈现出明显展宽且不对称的复合峰，主峰位于约294cm^-1，高频侧存在稳定的A₁^*肩峰（约305cm^-1），主峰半高宽（FWHM）为7.42cm^-1和11.46cm^-1，表明该类矿物总体保持黄铜矿型CuInS₂的基本结构，但局部存在由微量Fe、Zn置换引起的有限局域阳离子无序。结合寄主硫化物的微量元素特征、时间分辨率曲线、硫铟铜矿矿物学特征及其与自然银、自然铋等中-低温标型矿物组合特征，本文认为都龙锡锌铟多金属矿床中铟的富集经历了早期中-高温阶段在闪锌矿等硫化物晶格中分散赋存和晚期中-低温阶段形成独立矿物的过程，其中250~300℃可能是铟由类质同象状态向独立矿物相转变的关键温度窗口。对比国内典型硫铟铜矿产地表明，其形成与中生代岩浆-热液成矿作用、含Cu硫化物组合以及局部Cu-In-S富集有关。都龙矿区来龙矿段硫铟铜矿的发现填补了该矿床铟独立矿物研究的空白，为认识该类矿床中铟的赋存状态演化及富集过程提供了新的矿物学证据。