Major elements geochemistry of manganese nodules and ferromanganese crusts from the Pacific Ocean

Experimental substitutions of transition and alkaline earth cations into synthetic 10angstrom(Na-)-manganate show that cation uptake and the stability of the cation-substituted mineral increase with stability of the hydroxide of the cation. Hydrothermal treatment of synthetic 10angström-manganates with different metal contents as well as marine diagenetic and hydrothermal 10angstrom-manganates shows that the stabilities of their structures are enhanced with increasing temperature. The stabilization is due to reinforcement of the "tunnel" walls supporting the [Mn4+O62-] octaheral layers. The diagenetic 10angström-manganates have initially unstable buserite-like structures with each interlayer wall composed of two [Mn2+O3+x2-(OH-)3-x] octahedra (0 less-than-or-equal-to x less-than-or-equal-to 3) with either a [Na+O2x2-(OH-)n-2x] unit (n = 6 and/or 8) or less frequently a [Mn2+O2x2-(OH-)6-2x] octahedron in between. Some of these cations in the walls are post-depositionally substituted by highly hydrated divalent metal cations, particularly Cu2+ and Ni2+, while some of the Mn2+ ions are slowly oxidized to Mn4+. These interlayer changes result in higher crystal field stabilization energy and shifts from interlayer Van der Waal's forces and weak coordination links to strong coordination links which stabilize the mineral structures. Low-temperature hydrothermal 10angstrom-manganates have todorokite-like structures with "tunne"' walls constructed predominantly of [Mn2+O3+x2-(OH-)3-x] and [Mn2+O2x2-(OH-)6.2x] octahedra. High-temperature hydrothermal 10angstrom-manganates have stable todorokite structures with the walls constructed of [Mn4+O62-] octahedra. The positive correlation between the formation or post-depositional alteration temperatures and the mineral stability is due to the increase in oxidation rate of interlayer Mn2+ ions with increasing temperature of the hydrothermal fluids. Marine 10angstrom-manganates can be used as genetic indicators for manganese concretions and the sediments in which they occur and as a geothermometer in the search of ancient and modern hydrothermal vents, where massive sulphide deposits are often found.

将过渡金属与碱土金属阳离子实验取代合成10埃（10ångström）锰酸盐的研究结果表明，阳离子吸附量与阳离子取代矿物的稳定性，随该阳离子氢氧化物的稳定性升高而增强。对不同金属含量的合成10埃锰酸盐，以及海洋成岩型和热液型10埃锰酸盐开展水热处理，结果显示其结构稳定性随温度升高而提升。该稳定化效应源于支撑[Mn⁴⁺O₆²⁻]八面体层的“隧道”壁得到强化。海洋成岩型10埃锰酸盐初始具有不稳定的布塞尔矿（buserite）型结构，其层间壁由两个[Mn²⁺O₃+x²⁻(OH⁻)₃−x]八面体构成，八面体之间通常存在[Na⁺O₂x²⁻(OH⁻)ₙ−2x]单元（n=6和/或8），少数情况下则为[Mn²⁺O₂x²⁻(OH⁻)₆−2x]八面体。壁体中的部分阳离子会在沉积后被高水合二价金属阳离子（尤其是Cu²⁺与Ni²⁺）取代，同时部分Mn²⁺离子会缓慢氧化为Mn⁴⁺。这些层间变化会提升晶体场稳定能，并使层间相互作用从范德华力与弱配位键转变为强配位键，从而稳定矿物结构。低温水热成因的10埃锰酸盐具有类钙锰矿（todorokite）结构，其“隧道”壁主要由[Mn²⁺O₃+x²⁻(OH⁻)₃−x]与[Mn²⁺O₂x²⁻(OH⁻)₆−2x]八面体构筑而成。高温水热成因的10埃锰酸盐则具有稳定的钙锰矿（todorokite）结构，其壁体由[Mn⁴⁺O₆²⁻]八面体构筑而成。矿物形成或沉积后蚀变的温度与矿物稳定性之间的正相关关系，源于热液流体温度升高会加快层间Mn²⁺离子的氧化速率。海洋10埃锰酸盐可作为锰结核及其赋存沉积物的成因指示剂，同时也可作为寻找古代与现代热液喷口（该区域常产出块状硫化物矿床）的地质温标。