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81.
82.
The limitations of pulp chemistry measurements in the flotation of a platinum group mineral (PGM) bearing Merensky ore were demonstrated in Part 1 of this article. In this paper the importance of the contribution of the froth structure due to changing froth stability is analysed using the batch flotation data. The effects of mild steel (MS) and stainless steel (SS) milling media and the addition of copper sulphate on the flotation performance of the sulphide minerals in Merensky ore have been evaluated in relation to the changes in stability of the froth phase. The effects of pulp chemistry and froth stability on the flotation of sulphide minerals were distinguished by using two different rate constants (kt and kw). The rate constant (kw) calculated as a function of cumulative water recovery was used to describe characteristics of froth phase and kt was calculated as a function of flotation time. The results revealed that the type of grinding media and copper sulphate addition had an interactive effect on the froth stability. While mild steel (MS) milling increased the froth stability due to the presence of hydrophilic iron hydroxides and colloidal metallic iron, the addition of copper sulphate reduced the stability, especially with stainless steel (SS) milling. Copper sulphate addition had a dual role in the flotation of Merensky ore in that it caused destabilisation of the froth zone as well as activation of selected sulphide minerals. The dominant effect was found to depend on the type of milling media and floatability of the mineral in question and this work has demonstrated the importance of using a combination of measurements to evaluate flotation performance holistically. 相似文献
83.
Infrared microthermometry of opaque minerals has revealed that temperatures of phase changes vary with the infrared light source intensity, resulting in an overestimate of fluid salinities and an underestimate of homogenization temperatures. Failing to recognize this analytical artifact during infrared microthermometry may result in meaningless geological models. A fluid inclusion investigation on enargite from a high-sulfidation epithermal deposit is used as an example to document this. Fluid salinities obtained during an early investigation ranged between 6.3 and 20.4 wt.% NaCl, which were interpreted as intense boiling or as evidence for the involvement of a magmatic brine during ore formation. Fluid inclusion salinities obtained with improved analytical settings, i.e. low light intensities, fall between 1.1 and 1.7 wt.% NaCl and are in better agreement with fluid salinities obtained in quartz from similar deposits, and recent modeling suggesting vapor transport of Au and Cu from deep porphyry-Cu environments to shallower high-sulfidation epithermal deposits. 相似文献
84.
Besides granites of the ilmenite series, in which the anisotropy of magnetic susceptibility (AMS) is mainly controlled by paramagnetic minerals, the AMS of igneous rocks is commonly interpreted as the result of the shape-preferred orientation of unequant ferromagnetic grains. In a few instances, the anisotropy due to the distribution of ferromagnetic grains, irrespective of their shape, has also been proposed as an important AMS source. Former analytical models that consider infinite geometry of identical and uniformly magnetized and coaxial particles confirm that shape fabric may be overcome by dipolar contributions if neighboring grains are close enough to each other to magnetically interact. On these bases we present and experimentally validate a two-grain macroscopic numerical model in which each grain carries its own magnetic anisotropy, volume, orientation and location in space. Compared with analytical predictions and available experiments, our results allow to list and quantify the factors that affect the effects of magnetic interactions. In particular, we discuss the effects of (i) the infinite geometry used in the analytical models, (ii) the intrinsic shape anisotropy of the grains, (iii) the relative orientation in space of the grains, and (iv) the spatial distribution of grains with a particular focus on the inter-grain distance distribution. Using documented case studies, these findings are summarized and discussed in the framework of the generalized total AMS tensor recently introduced by Cañon-Tapia (Cañon-Tapia, E., 2001. Factors affecting the relative importance of shape and distribution anisotropy in rocks: theory and experiments. Tectonophysics, 340, 117–131.). The most important result of our work is that analytical models far overestimate the role of magnetic interaction in rock fabric quantification. Considering natural rocks as an assemblage of interacting and non-interacting grains, and that the effects of interaction are reduced by (i) the finite geometry of the interacting clusters, (ii) the relative orientation between interacting grains, (iii) their heterogeneity in orientation, shape and bulk susceptibility, and (iv) their inter-distance distribution, we reconcile analytical models and experiments with real case studies that minimize the role of magnetic interaction onto the measured AMS. Limitations of our results are discussed and guidelines are provided for the use of AMS in geological interpretation of igneous rock fabrics where magnetic interactions are likely to occur. 相似文献
85.
R. Thomas J.D. Webster D. Rhede W. Seifert K. Rickers H.-J. Frster W. Heinrich P. Davidson 《Lithos》2006,91(1-4):137-149
Fractional crystallization of peraluminous F- and H2O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions.
We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters. 相似文献
86.
Atomistic calculations of structural and elastic properties of serpentine minerals: the case of lizardite 总被引:1,自引:0,他引:1
A.-L. Auzende R. J.-M. Pellenq B. Devouard A. Baronnet O. Grauby 《Physics and Chemistry of Minerals》2006,33(4):266-275
The physical properties of the hydrous phyllosilicate lizardite have been investigated by atomistic simulation using the GULP code based on transferable semi-empirical interatomic potentials. Lizardite behavior was first investigated during structure relaxation at room temperature. The Helmholtz free energy is minimum for an equilibrium structure that is in agreement with experiment. The bulk, shear, and Young modulii for lizardite were calculated along with the Poisson ratio. From the shear and bulk modulii, we also calculated translational and longitudinal acoustic wave velocities that are important quantities for tectonophysics models. As expected, lizardite is stiffer in the a direction parallel to the layers than in the c perpendicular direction; the variation of the unit cell parameters with pressure is in good agreement with experiment. The cohesive energy between two successive layers along c direction was calculated at 0.33 eV (i.e., 0.11 eV per OH bond) in good agreement with recent ab initio calculations. Upon pressure and temperature variations, we evidenced that structural changes are mainly pressure induced; pressure being accommodated by a decrease of the c parameter up to 10 GPa. We also found that the change of slope in the derivative of the c cell parameter with respect to pressure occurring around 2 GPa originates from the bending of the interlayer hydroxyl groups with respect to the layer normal direction. 相似文献
87.
华南扬子地块是我国古热水沉积成矿作用最为发育的地区之一,其热水沉积特性最早引起我国学者的关注。华南下寒武统黑色岩系中赋存多个与热水沉积成矿作用相关的大型、超大型重晶石矿床与N i-Mo-U-V多金属富集层。进一步研究分布在华南扬子地块黑色岩系中的金属、非金属矿床成因及其地球化学特征,对认识华南乃至全球晚震旦—早寒武世生物与环境演化有着十分重要的意义。本文对华南下寒武统镍-钼富集层矿石进行电子探针研究,识别出黄铜矿、黝铜矿等铜的独立矿物;闪锌矿等锌的独立矿物;方铅矿、白铅矿等铅的独立矿物。研究表明,在镍-钼矿石中这些矿物的发现为镍-钼矿层是热水沉积作用产物提供了直接的矿物学证据。 相似文献
88.
89.
内蒙古中部重、磁场特征与地壳密度结构 总被引:2,自引:2,他引:2
中亚造山带中的古生代——中生代花岗岩普遍具有正εNd值,在世界上是十分独特的。美国西部加利福尼亚中生代-新生代花岗岩同样具有正εNd值,并且其地壳的速度分布特征与内蒙古中部十分相似。本文通过与美国加利福尼亚的地球物理研究成果进行对比,来研究内蒙古中部的地壳密度结构,特别是下地壳的组成,试图探讨产生正£。值花岗岩的深部地质原因。研究结果表明,在大兴安岭-内蒙古造山带下地壳中可能存在与美国加里福尼亚类似的洋壳物质。此外,还对重、磁异常进行了处理,以确定蛇绿岩带的延展情况。由于在西拉木伦河附近存在切割至莫霍面的深断裂,结合地表出现的蛇绿岩带,故提出温都尔庙-西拉木伦河一线可能是内蒙古中部最重要的地质构造界线。 相似文献
90.
宁镇地区中更新世环境演变的沉积学研究 总被引:6,自引:0,他引:6
句容放牛山剖面ESR测年、粒度以及磁化率的研究结果表明,下蜀黄土作为一种受后生成土作用强烈的风尘堆积,其性状与北方黄土差别很大,主要表现为由于成壤作用及次生风化作用导致粘粒含量增多。该剖面揭示出本区中更新世 5个气候暖湿期,分别是 :15 9~ 16 3ka,192ka,195~ 198ka,2 0 3~ 2 30ka与 311~ 35 0ka。其中第一个相对暖湿期不十分明显,在大致同时期的深海氧同位素 (V2 1- 14 6孔 ) 6阶段当中为一个小的气候回暖波动,第 2、3、4气候暖湿期可大致与西峰黄土S2古土壤层所反映的气候温暖事件相对应,可与深海氧同位素 (V2 1- 14 6孔 )第 7氧同位素阶段大致相对比。其中,前 4个温暖期可大致与老虎山下蜀黄土的标准剖面自上而下的 4个埋藏古土壤层相对应。旧石器考古发掘发现 6、7层有石器,从剖面测年资料及各环境代用指标综合分析得出,当时为暖湿的生态环境(即第 5个气候暖湿期 ),较适宜人类活动,与南京汤山猿人洞研究结果相一致。东北地区庙后山下层文化 (14 0 0~2 30ka)以大石片石器为主,文化面貌兼有华北大小两个石器系统的特征。这与该遗址发掘的石器相类似,这可能说明至少在中更新世中期长江河道应在句容以南。 相似文献