Geochemistry of Rare Earth Elements in Lamprophyres in Laowangzhai Gold Orefield, Yunnan Province

Lamprophyres, widely distributed in the Laowangzhai gold orefield, Yunnan province, China, and closely related to gold mineralization in time and space, can be distinguished into three kinds: the fresh (weakly altered ), the altered, and the mineralized lamprophyres. These lamprophyres in the orefield are similar in the range of BEE contents and REE patterns, but definitely different in parameters of LRE/HRE, NLa/Yb etc. The geochemistry of REE in fresh lamprophyre shows flat the rock is a product of different partial melting of the enriched mantle. Calculation results of mass balance of REE activity regularity in the process of alteration and mineralization of the lalnprophyres in the orefield shows that the altering fluids and mineralizing fluids contain REE, and these fluids are mainly [he products of mantle degassing and magma degassing during the lamprophyric magmatism.

Rare-Earth Elements and Genesis of Lamprophyres in the Laowangzhai Gold Orefield, Yunnan Province

The Laowangzhai super-large gold orefield, which is situated in northern Mt. Ailaotectonic zone, Yunnan Province, is a typical gold orefield where lamprophyres are temporallyand spatially related to gold mineratization. Major element data show that lamprophyres in theorefield are of alkalic series and can be divided into potassic and K-rich calc-alkaline lamprophyres. The rocks are enriched in rare-earth elenlents as compared with the primary mantle andmid-ocean ridge basalts(MORB). Modelled calculations by the least squares method of Petrological Mixing show that the mantle source for the lamprophyres is enriched in rare-earth elements. The geotectonic development of western Yunnan, Sr and Nd isotopic compeitions, incompatible element patterns and linear programing calculations indicate that the fluids were de-rived from dehydration of submaine sediments which are enriched in ALK, LREE and incompatible elements and then were carried to mantle wedges as a result of plate subduction. That isthe main factor leading to the formation of a metasomatic fertile mantle in the area studied.

The Sr, Nd isotopic composition of lamprophyres in Laowangzhai gold orefield, Yunnan Province

Lamprophyres are widely spread over the Laowangzhai gold orefield in northern Mt. Ailao structure zone, Yunnan Province. Lamprophyres in the orefield are temporally and spatially related to gold mineralization. Lamprophyres in the orefield have anomalous Sr and Nd isotopic compositions, e.g. the 87Sr/ 86Sr ratios (0.706 665-0.707 960, the 87Sr/ 86Sr ratio of sample YLW-44 is 0.709 041) are higher than the modern value of the original mantle (0.704 5), the 143Nd/ 144Nd ratios (0.512 463-0.512 551) are lower than the modern value of the original mantle (0.512 638), and the calculated values ε Sr>0 (28.1-63.7) and ε Nd<0 (-1.34--3.07). The results of investigation indicate that lamprophyres in the Laowangzhai gold orefield with anomalous Sr and Nd isotopic compositions would not be produced as a result of contamination of the primary magma with the isotopic features of MORB by the crust materials high 87Sr/ 86Sr ratios and low 143Nd/ 144Nd ratios in the processes of rising or in the magma chamber, but the result of metasomatism of source mantle.

云南老王寨金矿区煌斑岩中云母的矿物化学

云南老王寨金矿区煌斑岩中呈斑晶和基质产出的云母以金云母为主，少量富镁黑云母，环带结构发育。矿物化学表明本区云母的寄主岩石属碱性岩系列，岩石类型为钙碱性煌斑岩；同时提供了煌斑岩源于交代富集地幔和受地壳物质混染程度低等成因信息。云母多种多样的环带结构暗示其寄主的煌斑岩具复杂的岩浆结晶演化过程。

云南老王寨金矿区煌斑岩的源区成分模拟

本文在总结云南老王寨金矿区煌斑岩的主要元素、过渡元素、亲石元素、稀土元素和同位素地球化学特征的基础上．利用岩石学混合计算方法对其源区成分进行了模拟，进而讨论了矿区这类岩石的成因。地球化学和模拟计算均表明，老王寨金矿区煌斑岩来源于交代富集地幔，板块俯冲（印度板块向欧亚板块俯冲）富含ALK、LREE及不相容元素的海底沉积物被带入地幔脱水形成的流体是引起本区地幔交代作用的主要因素。

云南老王寨金矿煌斑岩固定铵(NH_4^+)地球化学特征

云南老王寨金矿与金矿化时空密切共生的煌斑岩可分为新鲜(弱蚀变)、蚀变和矿化3种。固定铵(NH_4^+)含量测定结果表明,新鲜煌斑岩固定铵含量明显高于其他幔源岩石、低于矿区碳质围岩的固定铵含量。笔者认为该特征可能不是地壳混染的结果,从新鲜煌斑岩→蚀变煌斑岩→矿化煌斑岩,固定铵含量递增,且与金含量具较好的正相关,表明矿区煌斑岩蚀变流体和矿化流体中均可能存在铵,铵在金矿化流体中对金的迁移起了作用。

介绍一套岩浆过程模拟软件──TRAZAS

介绍了一套岩浆过程模拟软件──TRAZAS的运行环境、设计基础、设计流程及主要功能，并以云南老王寨金矿区煌斑岩成因研究为例，简单说明了软件的运用。