在普查找矿中运用物化探的几点体会

去年,我们在某古老变质岩地区开展了以铜为主的普查找矿,这是以地质与物化探相结合的综合技术找矿工作。在磁法和次生晕圈定的成矿有望地段中,作了槽探揭露,局部矿化富集则用钻探作深部验证,打到了够工业品位的矿体,从而较快地体现出物化探的地质效果。我们的具体做法及工作体会是:     

关于坑探机械化现代化的探讨

一、坑探在探矿工作中的作用坑探是加速取得地质成果，提高地质工作质量的重要手段。地质人员除了用它揭露地表，验证物化探，配合钻探弄清矿体产状，求得储量外，在稀有金属、分散元素及不规则的矿体勘探方面，仍是一种主要手段。它的特点是能够直接观察现象和矿体产状，取样方便准确，有些探矿坑道，可提供采矿利用，起     

激电测量在寻找硅质角砾岩型铀矿中的应用

对硅质角砾岩型的320矿床的典型剖面进行综合物化探研究结果表明,这类矿床的隐伏铀矿体具有高值大范围的极化率(η_(?))异常,激电测深可圈定矿体的埋深、产状、规模等特征,激电法是寻找这类隐伏铀矿的高灵敏度方法。在这类矿体的地表还有γ,Po,He,Cu,Mo等物化探异常,根据这些综合异常可推断激电异常是否反映了隐伏铀矿体,大大提高物化探综合找矿的能力。对320矿区外围同类异常点进行综合物化探研究的结果,在WBC地区发现了大范围高值激电异常及其它综合物化探异常,而且地质条件、区域航测、重力、水化学、分散流等异常特征也与320矿区相似,预测为隐伏铀矿远景区。     

关于做好当前物化探工作的意见

冶金系统的物化探工作,通过几年的调整,技术队伍得到了巩固和发展,技术水平有所提高,在各种金属矿区中取得了显著的地质效果。随着地表地质工作的深入,以找露头、清理旧硐等地质测量方法已有了一定的局限性,必然的趋势是广泛应用物化探找矿方法,寻找隐伏矿体和深部盲矿体。物化探是用高精度仪器和高灵敏度微量分析来找矿,因此发展物化探方法已成为促进找矿工作现代化     

鄂伦春自治旗某农场金矿化探异常特征及找矿意义

在植被覆盖严重的大兴安岭林区找矿,通过物化探方法及地表槽探工程揭露、中浅部钻探工程验证已发现并圈定金矿体3条。实践证明,采用物化探及工程方法,是寻找植被覆盖严重区矿体的有效方法之一。     

物化探在新疆西昆仑铅锌矿预查中的应用

以已知矿体上物化探异常特征为依据,对区内其他物化探异常进行了分类与解释推断,圈定了四条矿化体.     

铅锌硫化物矿床物化探普查中几个问题的探讨

众所周知,寻找大而浅的硫化物金属矿床,用常规物化探方法就可以获得比较清晰的异常,而且辨认矿与非矿异常比较容易,因此,物化探普查的地质效果和经济效益是比较显著的。然而,目前物化探面临的主要任务是寻找埋藏较深的盲矿体。在新的情况下,如何提高物化探的找矿效果和经济效益,是物化探找矿工作急待解决的问题。本文试图通过湘南热液铅锌硫化矿床物化探找矿效果的总结研究,对寻找深部盲矿体和识别电法矿异常与非矿异常两个问题进行探讨。     

物化探在保山核桃坪矿床中的综合应用

核桃坪铅锌铜多金属矿的靶区选择、评价及矿床发现中,由浅入深的物化探工作,在8个综合物化探异常区都找到多金属硫化物矿体,金厂河矿区实现隐伏深部找矿的重大突破。并总结出了一套合理的找矿勘查技术。     

内蒙古呼扎盖吐钼矿床物化探异常特征及找矿效果

呼扎盖吐钼矿床是验证物化探异常而发现的一座斑岩型矿床,矿体主要赋存在燕山早期细粒花岗岩与中奥陶统汉乌拉组流纹岩内接触带附近。矿区内物化探异常围绕花岗岩岩体分布,套合良好,层次结构清晰,中心部位为正值高磁区,向外依次为负值低磁区及土壤异常、正值低磁区及激电异常、负值正常磁场。物化探异常对岩体及矿体有良好的指示作用,磁异常反映了含矿花岗岩岩体及矿化蚀变分布范围,土壤异常反映了钼矿体赋存部位,激电异常反映了岩体接触带附近钼矿体及强黄铁矿化流纹岩的分布地段。槽探和钻探验证物化探异常已圈出3处钼矿化带,发现5条钼矿体及3条钼矿化体。获得的钼资源量已达中型,矿床具有大型成矿远景。     

吉林省伊通县小黑顶子银矿地质特征及找矿标志

本地区通过对物化探资料的综合整理及地表工程的验证,在调查区大致查明了成矿地质条件,大致控制了主要矿体特征。区内新发现银矿(化)体3条,银矿(化)体受北西向断裂构造控制,矿石类型为石英脉。此次目的是通过地质工作和物化探工作的综合研究,找出该矿产地不同岩性中物理性质和化学性质的特征,总结出矿体的成矿规律,为进一步工作以及寻找同类型矿种提供线索。     

Low-temperature heat capacities of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and spinels of the MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript>–MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> solid solution

We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl₂O₄ and MgCr₂O₄. The data also include new low-temperature heat capacity measurements for MgAl₂O₄ spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed for MgAl₂O₄ spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)₂O₄ spinels. We suggest a standard entropy for MgAl₂O₄ of 80.9 ± 0.6 J mol⁻¹ K⁻¹. For the solid solution between MgAl₂O₄ and MgCr₂O₄, we observe a linear increase of the standard entropies from 80.9 J mol⁻¹ K⁻¹ for MgAl₂O₄ to 118.3 J mol⁻¹ K⁻¹ for MgCr₂O₄.     

Point defects and cation tracer diffusion in (Ti<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Fe<Subscript><Emphasis Type="Italic">1−x</Emphasis></Subscript>)<Subscript>3−δ</Subscript>O<Subscript>4</Subscript>. II. Cation tracer diffusion

 Cation tracer diffusion coefficients, D_Me ^*, for Me=Fe, Mn, Co and Ti, were measured using radioactive isotopes in the spinel solid solution (Ti _x Fe _1−x )_3−δO₄ as a function of the oxygen activity. Experiments were performed at different cationic compositions (x=0, 0.1, 0.2 and 0.3) at 1100, 1200, 1300 and 1400 °C. The oxygen activity dependence of all data for D_Me ^* at constant temperature and cationic composition can be described by equations of the type D_Me ^*=D^∘ _Me[V]. C_V·a _O2 ^2/3+D_Me[I] ^∘·a _O2 ^−2/3·D_Me[V] ^∘ and D_Me[I] ^∘ are constants and C_V is a factor of the order of unity which decreases with increasing δ. All log D_Me ^* vs. loga _O2 curves obtained for different values of x and for different temperatures go through a minimum due to a change in the type of point defects dominating the cation diffusion with oxygen activity. Cation vacancies prevail for the cation diffusion at high oxygen activities while cation interstitials become dominant at low oxygen activities. At constant values of x, D_Me[V] ^∘ decreases with increasing temperature while D_Me[I] ^∘ increases.     

LiFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and NaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript> at low temperatures: an infrared spectroscopic study

 Synthetic aegirine LiFeSi₂O₆ and NaFeSi₂O₆ were characterized using infrared spectroscopy in the frequency range 50–2000 cm⁻¹, and at temperatures between 20 and 300 K. For the C2/c phase of LiFeSi₂O₆, 25 of the 27 predicted infrared bands and 26 of 30 predicted Raman bands are recorded at room temperature. NaFeSi₂O₆ (with symmetry C2/c) shows 25 infrared and 26 Raman bands. On cooling, the C2/c–P2₁/c structural phase transition of LiFeSi₂O₆ is characterized by the appearance of 13 additional recorded peaks. This observation indicates the enlargement of the unit cell at the transition point. The appearance of an extra band near 688 cm⁻¹ in the monoclinic P2₁/c phase, which is due to the Si–O–Si vibration in the Si₂O₆ chains, indicates that there are two non-equivalent Si sites with different Si–O bond lengths. Most significant spectral changes appear in the far-infrared region, where Li–O and Fe–O vibrations are mainly located. Infrared bands between 300 and 330 cm⁻¹ show unusually dramatic changes at temperatures far below the transition. Compared with the infrared data of NaFeSi₂O₆ measured at low temperatures, the change in LiFeSi₂O₆ is interpreted as the consequence of mode crossing in the frequency region. A generalized Landau theory was used to analyze the order parameter of the C2/c–P2₁/c phase transition, and the results suggest that the transition is close to tricritical. Received: 21 January 2002 / Accepted: 22 July 2002     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

BaCO<Subscript>3</Subscript>: high-temperature crystal structures and the <Emphasis Type="Italic">Pmcn</Emphasis>→<Emphasis Type="Italic">R</Emphasis>3<Emphasis Type="Italic">m</Emphasis> phase transition at 811°C

The temperature (T) evolution of the barium carbonate (BaCO₃) structure was studied using Rietveld structure refinements based on synchrotron X-ray diffraction and a powdered synthetic sample. BaCO₃ transforms from an orthorhombic, Pmcn, α phase to a trigonal, R3m, β phase at 811°C. The orthorhombic BaCO₃ structure is isotypic with aragonite, CaCO₃. In trigonal R3m BaCO₃, the CO₃ group occupies one orientation and shows no rotational disorder. The average <Ba–O> distances increase while the <C–O> distances decrease linearly with T in the orthorhombic phase. After the 811°C phase transition, the <Ba–O> distances increase while C–O distances decrease. There is also a significant volume change of 2.8% at the phase transition.     

Atomistic model of diopside-K-jadeite (CaMgSi<Subscript>2</Subscript>O<Subscript>6</Subscript>-KAlSi<Subscript>2</Subscript>O<Subscript>6</Subscript>) solid solution

Atomistic model was proposed to describe the thermodynamics of mixing in the diopside-K-jadeite solid solution (CaMgSi₂O6-KAlSi₂O₆). The simulations were based on minimization of the lattice energies of 800 structures within a 2 × 2 × 4 supercell of C2/c diopside with the compositions between CaMgSi₂O₆ and KAlSi₂O₆ and with variable degrees of order/disorder in the arrangement of Ca/K cations in M2 site and Mg/Al in Ml site. The energy minimization was performed with the help of a force-field model. The results of the calculations were used to define a generalized Ising model, which included 37 pair interaction parameters. Isotherms of the enthalpy of mixing within the range of 273–2023 K were calculated with a Monte Carlo algorithm, while the Gibbs free energies of mixing were obtained by thermodynamic integration of the enthalpies of mixing. The calculated T-X diagram for the system CaMgSi₂O₆-KAlSi₂O₆ at temperatures below 1000 K shows several miscibility gaps, which are separated by intervals of stability of intermediate ordered compounds. At temperatures above 1000 K a homogeneous solid solution is formed. The standard thermodynamic properties of K-jadeite (KAlSi₂O₆) evaluated from quantum mechanical calculations were used to determine location of several mineral reactions with the participation of the diopside-K-jadeite solid solution. The results of the simulations suggest that the low content of KalSi₂O₆ in natural clinopyroxenes is not related to crystal chemical factors preventing isomorphism, but is determined by relatively high standard enthalpy of this end member.     

The crystal structure of alumoklyuchevskite,K<Subscript>3</Subscript>Cu<Subscript>3</Subscript>AlO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal structure of the unstable mineral alumoklyuchevskite K₃Cu₃AlO₂(SO₄)₄ [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R ₁ = 0.131 for 2450 unique reflections with F ≥ 4σF _hkl. The structure is based on oxocentered tetrahedrons (OAlCu ₃ ⁷⁺ ) linked into chains via edges. Each chain is surrounded by SO₄ tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K₃Cu₃Fe³⁺O₂(SO₄)₄; and piypite, K₂Cu₂O(SO₄)₂.     

First-principles-based calculations of the CaCO<Subscript>3</Subscript>–MgCO<Subscript>3</Subscript> and CdCO<Subscript>3</Subscript>–MgCO<Subscript>3</Subscript> subsolidus phase diagrams

 Planewave pseudopotential calculations of supercell total energies were used as bases for first-principles calculations of the CaCO₃–MgCO₃ and CdCO₃–MgCO₃ phase diagrams. Calculated phase diagrams are in qualitative to semiquantitative agreement with experiment. Two unobserved phases, Cd₃Mg (CO₃)₄ and CdMg₃(CO₃)₄, are predicted. No new phases are predicted in the CaCO₃–MgCO₃ system, but a low-lying metastable Ca₃Mg(CO₃)₄ state, analogous to the Cd₃Mg(CO₃)₄ phase is predicted. All of the predicted lowest-lying metastable states, except for huntite CaMg₃(CO₃)₄, have dolomite-related structures, i.e. they are layer structures in which A _m B _n cation layers lie perpendicular to the rhombohedral [111] vector. Received: 6 May 2002 / Accepted: 23 October 2002 Acknowledgements This work was partially supported by NSF contract DMR-0080766 and NIST.     

Raman spectroscopic study of hydrous <Emphasis Type="Italic">γ</Emphasis>-Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> to 56.5 GPa

 Raman spectra of a single-crystal fragment of hydrous γ-Mg₂SiO₄, synthesized in a multianvil press, have been measured in a diamond-anvil cell with helium as pressure-transmitting medium to 56.5 GPa at room temperature. All five characteristic spinel Raman modes shift continuously up to the highest pressure, showing no evidence for a major change in the crystal structure despite compression well beyond the stability field of ringwoodite in terms of pressure. At pressures above ∼30 GPa a new mode on the low-frequency site of the two silicate-stretching modes is clearly identifiable, indicating a modification in the spinel structure which is reversible on pressure release. The frequency of the new mode (802 cm⁻¹ extrapolated to 1 bar) suggests the presence of Si–O–Si linkages and/or a partial increase in the coordination of Si. Direct determination of the subtle structural change causing the new Raman mode would require high-pressure, single-crystal synchrotron X-ray diffraction experiments. The Raman modes of hydrous and anhydrous Mg-end-member ringwoodite are nearly identical up to 20 GPa, suggesting that protonation has only minor effect on the lattice dynamics over the entire pressure stability range for ringwoodite in the mantle. Received: 7 December 2001 / Accepted: 16 April 2002