美国内华达卡林金矿之含金FeS2微晶中不可见金的TEM研究和地球化学模型

透射电子显微术的研究表明，美国内华达州卡林金矿中环绕黄铁矿大 晶体的Fe的硫 化物微晶乃是白铁矿。该白铁矿含Au和As，并在其中有纳米尺度的似带状区。相对于邻区 而言，似带状区相对富As。因而提出：似带状区还相对富晶格金。根据所得出的方解石中三 价阳离子的分配系数方程认为，Au3＋阳离子是在白铁矿的非平衡(快速)结晶 作用期间，从白铁矿－溶液界面上被结合到细粒白铁矿中去的。Au3＋在白铁矿中的 配分是由非平衡分布系数(Kd')所控制的。然而，由于Au 3＋的平衡分 配系数(Kd)小，故通过平衡(缓慢)结晶作用形成的黄铁矿并不将Au 3 ＋结合到晶体中去。早期形成的细粒晶体的再结晶作用则将把REE和Au从晶体中迁移走。 相对于正常的白铁矿结构而言，较大的Au3＋和Au＋阳离子结合进入到白铁矿晶格 中，可引起局部的结构畸变，从而表现为似带状的特征。

Investigation of Invisible Au in Au-bearing FeS_2 Microcrystals from Carlin Gold Ore Deposit, Nevada, USA:TEM Study and Geochemical Modeling

Transmission electron microscopy study indicates that microcrystalline Fesulfide crystals around large pyrite crystals from Carlin mine of Nevada are marcasite. The marcasite contains Au and As. There are bandlike features in the marcasite. These bandlike areas are relatively rich in As with respect to the neighboring areas. It is proposed that the bandlike areas are also relatively rich in lattice bound Au. According to the obtained equation for distribution coefficients of trivalent cations in calcite, it is proposed that cationic Au 3 were incorporated into the fine grain marcasite at the marcasite-solution interface during non equilibrium (fast) crystallization of the marcasite. The partitioning of Au 3 in the marcasite is controlled by non equilibrium distribution coefficient (K ' d). However, pyrite formed through equilibrium (slow) crystallization will not incorporate Au 3 into the crystal, because of its low equilibrium distribution coefficient (K d) for Au 3 . Recrystallization of early formed fine grain crystals will remove REE and Au from the crystals. Incorporation of larger cations of Au 3 and Au may result in local structural distortion with respect to normal marcasite structure, and shows the form of the band like feature.