Thermodynamics and crystal chemistry of copper arsenates

矿床和矿点的氧化带可以自然形成，也可以人为作用形成。在这两种情况下，它们构成了地球表面附近形成和塑造矿物的自然过程的一个窗口，并决定了风化原生矿物周围矿物、元素和生物群的命运。在这个提案中，我计划将重点放在铜砷酸盐矿物上，这是一种在许多氧化带中遇到的惊人变化的矿物组。它们能够固定或释放铜、砷和其他元素，如Pb、Zn或Se。在本研究中，我们将通过结合酸溶液（生成焓）和弛豫（熵）量热法来确定砷酸铜矿物（黄铜矿、橄榄石、辉石、闪石、闪石、闪石和常铬铁矿）的端元和固溶体的热力学性质。选定的固溶体的混合参数将通过量热法或溶解度研究得出，并用于构建李普曼图，以显示固溶体和水相之间相互作用的性质。计算出的混相间隙将与天然固溶体的组成（由电子探针确定）进行严格的比较。我们将开展实地工作，在实地收集砷酸铜矿物和共存的水溶液，并利用这些溶液的组成来得出所研究相的热力学性质的独立值。在建议工作的最后阶段，热力学结果和已知的砷酸铜晶体学模型将结合到一个数学模型中，该模型基于矿物中单个结构块（多面体）的能量分配，预测所有砷酸铜矿物的热力学性质。

Oxidation zones of ore deposits and ore occurrences can originate naturally or by a maninduced action. In either case, they constitute a window in the natural processes which form and shape minerals near the Earth¿s surface and determine the fate of minerals, elements, and biota around the weathering primary minerals. In this proposal, I am planning to focus on copper arsenate minerals, an astonishingly variable group of minerals encountered in many oxidation zones. They are capable of immobilizing or releasing copper, arsenic, and other elements, such as Pb, Zn, or Se. Within the proposed work, we will determine thermodynamic properties of endmembers and solid solutions of copper arsenate minerals (chalcophyllite, liroconite, strashimirite, tyrolite, parnauite, geminite, and euchroite) by a combination of acid-solution (enthalpy of formation) and relaxation (entropy) calorimetry. The mixing parameters for selected solid solutions will be derived by calorimetry or solubility studies and used to construct Lippmann diagrams that show the nature of the interaction between a solid solution and an aqueous phase. The calculated miscibility gaps will be critically compared to the composition of natural solid solutions (determined by electron microprobe). We will carry out field work, collect copper arsenate minerals and co-existing aqueous solutions in the field, and use the composition of these solutions to arrive at independent values of thermodynamic properties of the phases studied. In the final phases of the proposed work, the thermodynamic results andthe known crystallographic models for the copper arsenates will be combined into a mathematical model that predicts the thermodynamic properties of all copper arsenate minerals, based on the assignment of energies to the individual structural blocks (polyhedra) in the minerals.