Manganese Sturmanite from the N’Chwaning 2 Mine, Kalahari, South Africa

IF 0.8 4区地球科学 Q3 GEOLOGY

Geology of Ore Deposits Pub Date : 2023-12-01 DOI:10.1134/s1075701523070036

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引用次数: 0

Abstract

The oxidation state of Mn is determined for the first time by iodine titrimetry, and the Mn⁴⁺/Mn³⁺ ratio (54/46%) is identified for Mn-sturmanite from the N’Chwaning 2 Mine (Kalahari manganese field, South Africa). The Mössbauer spectrum of sturmanite, which contains a single asymmetric Lorentz doublet with parameters ^RTIS_α-Fe = 0.31(1) mm/s, ^RTQS = 0.18(1) mm/s, FWHM_L = 0.55 mm/s, and FWHM_R = 0.33 mm/s, confirms the presence of Fe³⁺ only in the composition of the mineral. The process of its thermal transformation is studied using thermal analysis and IR spectroscopy: dehydration and decomposition of Ca polyhedra, dehydroxylation, decarbonatization, and complete decomposition of structure with the formation of anhydrite, hematite, and Ca borates occur up to 200, 600, 750, and 1000°C, respectively. The chemical formula of the studied sturmanite, which is calculated on the basis of our studies per eight cations, is as follows: Ca_5.94 \({\text{Fe}}_{{1.03}}^{{3 + }}{\text{Mn}}_{{0.54}}^{{4 + }}{\text{Mn}}_{{0.44}}^{{3 + }}\) Al_0.03Si_0.02[B(OH)₄]_1.00[B(OH)₃]_0.11[SO₄]_2.32[СО₃]_0.49(OH)₁₂⋅22.7H₂O. The unit cell parameters of the mineral are determined using X-ray powder diffraction: a = 11.148(3) Å, c = 21.830(9) Å, and V = 2349(2) Å³. The unit cell parameters of minerals of the sturmanite–jouravskite series linearly decrease with an increasing mole amount of the jouravskite endmember. It is suggested that the studied mineral can be an intermediate member of the sturmanite–jouravskite series with heterovalent isomorphic substitution according to following schemes: Mn³⁺ and Mn⁴⁺ → Fe³⁺ in the cation octahedral site and [CO₃]^2– → [B(OH)₄]^– and [SO₄]^2– in the anion site.

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南非卡拉哈里N'Chwaning 2矿的锰黝帘石

摘要通过碘滴定法首次测定了锰的氧化态，并确定了N'Chwaning 2矿（南非卡拉哈里锰矿区）的锰-鲟石的Mn4+/Mn3+比率（54/46%）。鲟鱼石的莫斯鲍尔光谱包含一个不对称洛伦兹双特，参数为 RTISα-Fe = 0.31(1) mm/s，RTQS = 0.18(1) mm/s，FWHML = 0.55 mm/s，FWHMR = 0.33 mm/s。利用热分析和红外光谱对其热转化过程进行了研究：钙多面体脱水和分解、脱羟基、脱碳，以及结构的完全分解，形成无水石膏、赤铁矿和钙硼酸盐的温度分别高达 200、600、750 和 1000°C。根据我们对八种阳离子的研究，所研究的鲟鱼石的化学式计算如下：Ca5.94 \({text{Fe}}_{{1.03}}^{3 + }}{text{Mn}}_{{0.54}}^{4 + }}{text{Mn}}_{{0.44}}^{{3 + }}\)Al0.03Si0.02[B(OH)4]1.00[B(OH)3]0.11[SO4]2.32[СО3]0.49(OH)12⋅22.7H2O.该矿物的单胞参数是通过 X 射线粉末衍射测定的：a = 11.148(3) Å，c = 21.830(9) Å，V = 2349(2) Å3。黝帘石-黝帘石系列矿物的单胞参数随着黝帘石内含物摩尔量的增加而线性降低。根据以下方案，我们认为所研究的矿物可能是鲟鱼石-焦拉沸石系列的中间成员，具有异价同构取代作用：阳离子八面体位上的 Mn3+ 和 Mn4+ → Fe3+，阴离子位上的 [CO3]2- → [B(OH)4]- 和 [SO4]2-。

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来源期刊

Geology of Ore Deposits 地学-地质学

CiteScore

1.10

自引率

14.30%

发文量

审稿时长

6-12 weeks

期刊介绍： Geology of Ore Deposits is a periodical covering the topic of metallic and nonmetallic mineral deposits, their formation conditions, and spatial and temporal distribution. The journal publishes original scientific articles and reviews on a wide range of problems in theoretical and applied geology. The journal focuses on the following problems: deep geological structure and geodynamic environment of ore formation; distribution pattern of metallogenic zones and mineral deposits; geology and formation environment of large and unique metallic and nonmetallic deposits; mineralogy of metallic and nonmetallic deposits; physicochemical and isotopic characteristics and geochemical environment of ore deposition; evolution of ore-forming systems; radiogeology and radioecology, economic problems in exploring, developing, and mining of ore commodities.