陕西几类重要铅锌矿床的矿物微量元素和稀土元素特征

文章将陕西铅锌矿分为海底喷气沉积型(即SEDEX型)、与海底喷气沉积-改造作用有关的类SEDEX型和MVT型3类.对马元(MVT型)、南沙沟和江坡(类SEDEX型)、铅硐山和二里河(SEDEX型)铅锌矿床中的闪锌矿等矿物进行的微量元素和稀土元素测定结果表明,3类矿床各具特点:马元铅锌矿床闪锌矿的Co、Ni、Th、Y含量较低,而Mo、Cs、Sr、Ba、T1含量较高;南沙沟和江坡铅锌矿床闪锌矿的Sn、Sb、W含量较低,而Mn、Y、Zr、In含量较高;铅硐山和二里河铅锌矿床闪锌矿的Li、Zr、CB、Ba含量较低,而W含量较高;在闪锌矿Li-Cs、Zr-In、W-Sn、∑REE-δEu、δEu-δCe散点图上,5个矿床的投点按上述3类分别集中.但铅硐山和二里河铅锌矿床与南沙沟和江坡铅锌矿床具有更多的相似性,而与马元铅锌矿床差异较大:在闪锌矿Sr-Ba、Co-Ni、Th-Y、Mo-T1散点图上,马元的投点集中于一处,而其他4个矿床的投点集中于另一处;马元闪锌矿具有十分明显的铕正异常,而南沙沟、江坡、铅硐山和二里河闪锌矿铕异常不明显,或具有负铕异常;5元素矿床闪锌矿稀土元素配分曲线均为轻稀土元素稍富集的右倾型,但马元的稀土元素总量明显低于其他4个矿床.

Characteristics of trace and rare earth elements in minerals from some typical lead_zinc deposits of Shaanxi Province

There are three types of Pb-Zn deposits in Shaanxi Province. The most important type is hosted in Devonian strata of the South Qinling orogenic belt and is classified as SEDEX, like the Qiandongshan lead-zinc deposit and the Erlihe lead-zinc deposit (also known as the Bafangshan lead-zinc deposit). The second type is hosted in Silurian strata of the same orogenic belt and is classified as SEDEX-like, represented by the Nanshagou lead-zinc deposit and the Jiangpo lead-zinc deposit. The third type is the Mayuan lead-zinc deposit discovered recently in the dolomitite of the Sinian Dengying Formation on the northern margin of Yangtze craton, belonging to MVT. In order to study the trace and rare earth element characteristics of these three types of lead-zinc deposits, the authors determined trace element and REE contents of sphalerite, calcite, galena and chaleopyrite from Mayuan, Nanshagou, Jiangpo, Qiandongshan and Erlihe lead-zinc deposits by using ICP-MS. The results suggest that different types of lead-zinc deposits have different trace and rare earth element characteristics. The sphalerite from the Mayuan lead-zinc deposit has low content of Co, Ni, Th and Y and high content of Mo, Cs, Sr, Ba and Tl. The sphalerite from Nanshagou and Jiangpo lead-zinc deposits has low content of Sn, Sb and W, high content of Mn, Y, Zr and In and in some cases high content of Li, Ni, Rb and Nb. The sphalerite from Qiandongshan and Erlihe lead-zinc deposits has low content of Li, Zr, Sr and Ba and high content of W. In Li-Cs, Zr-In, W-Sn, ΣREE-δEu and δEu-δCe diagrams of sphalerite, the five lead-zinc deposits are clustered in three or four regions in type. However, Qiandongshan and Erlihe Pb Zn deposits (SEDEX) and Nanshagou and Jiangpo Pb-Zn deposits (SEDEX-like) are comparatively similar to each other but obviously different from the Mayuan Pb-Zn deposit (MVT). InCo-Ni, Th-Y, Sr-Ba, Mo-Tl diagrams of sphalerite, the dots of Mayuan are clustered in one area while the dots of the other four deposits are clustered in another area. Chondrite-normalized REE patterns of sphalerite from the five deposits are all slightly right oblique, suggesting LREE enrichment. Nevertheless, ΣREE values of sphalerite from Mayuan are much lower than the values of the other four deposits. Mayuan sphalerite has very obvious positive Eu anomaly, whereas the sphalerite from Nanshagou, Jiangpo, Qiandongshan and Erlihe lead-zinc deposits does not show obvious Eu anomaly or negative Eu anomaly.