The ‘orogenic andesite’ puzzle of C. E. Tilley: 1—Is the volatile phase the missing piece?     

R. L. Stanton 《Australian Journal of Earth Sciences》2013,60(5):625-641

Some 65 years ago, C. E. Tilley, in his 1950 Presidential Address to the Geological Society of London, brought into sharp focus the then perhaps-not-fully-recognised problem of the origin of what he termed the ‘orogenic andesites’—and, in particular, their commonly constituent calc-alkaline lineage of lavas and pyroclastic materials. In spite of much investigation and progress since, the problem remains not fully resolved. The two most conspicuous features of such orogenic—i.e. island arc—volcanism are its copious, explosive, degassing and, as Tilley noted, its copious development of andesites and their more felsic associates. If these rock types were derived from basalt, the principal relevant changes in major element composition are reductions in Fe, Ca and Mg, and increases in Si, Al and (Na + K). Four principal mechanisms for inducing these changes have been proposed: (1) magmatic differentiation induced by fractional crystallisation, (2) magma mixing, (3) partial melting of an ultramafic-derived basaltic parent, and (4) crustal contamination. A fifth postulate—long recognised but only occasionally seriously considered—is that loss in the volatile phase during eruption and later degassing may make a significant contribution to the overall process. On the basis that Tilley's (and others’) orogenic basalt–andesite–dacite–rhyolite series constitutes a linear arrangement on the conventional FeO_t–MgO–(Na₂O + K₂O) diagram it is shown on numerical grounds that fractional crystallisation alone cannot account for the observed compositional trend—that, while accumulates are neither uncommon nor insubstantial in amount in modern arcs, they are olivine-rich, not magnetite-rich, and that numerical, petrological and field evidence indicates that the high oxidation/magnetite subtraction hypothesis of orogenic andesite genesis can no longer be seriously entertained. The partial melting hypothesis encounters contrary numerical evidence, closely analogous with that adduced for fractional crystallisation. Magma mixing eventually encounters the difficulty of the nature of the felsic material required for rhyolite formation, and assimilation of the preservation of primitive isotope ratios as lava evolution progresses. A fifth mechanism—volatile loss—may make a significant contribution to the relevant compositional change, perhaps in combination with one or more of the other proposed processes. Geochemical, petrological and field evidence pertaining to this is reviewed and examined, and it is postulated that indeed a combination of fractional crystallisation as the principal mechanism, volatile loss as a contributing factor, provides a plausible process. A case is made for an exploratory experimental investigation of the possibility of significant loss in a gas/vapour phase.  相似文献   

The effect of hydrodynamic conditions on true flotation and entrainment in flotation of a complex sulphide ore     

Emin Cafer Cilek   《International Journal of Mineral Processing》2009,90(1-4):35-44

The separation efficiency and selectivity of flotation are directly proportional to recoveries of the mineral species in the feed due to true flotation and entrainment. In this study, effects of the hydrodynamic conditions on true flotation and entrainment were investigated by using a fractional factorial experimental design. A method previously described in the literature was applied to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore. In order to apply the method, the kinetic flotation tests were conducted under various hydrodynamic conditions defined by some physical variables. Some of these tests were conducted in the presence and absence of a collector to evaluate the self-induced floatability. The selectivity index of the mineral species for entrainment was seen to be suitable evaluation of the non-selectivity and efficiency of the entrainment. Furthermore, the results of the size-by-size analysis of the froth products indicated that the presence of the self-induced hydrophobic particles in the feed is as important as the presence of very fine particles for accurate estimation of true flotation and entrainment in flotation of a complex sulphide ore. In addition, the estimated results for entrainment in flotation of the complex sulphide ore can be misleading. Therefore, a new approach would be necessary to determine the contributions of true flotation and entrainment in flotation of a complex sulphide ore.  相似文献   

Variations of Ag/Au ratios in hydrothermal ore bodies     

V. G. Nevstruev 《Russian Journal of Pacific Geology》2009,3(1):91-98

The analysis of the Ag and Au contents in ore bodies of different formation types reveals that the Ag/Au ratio functionally depends on the relative sulfide index of the ores (the ratio between the product of the Pb, Zn, and Cu content and the gold content). The functional dependence is best approximated by a power function. Based on 85 geochemical characteristics of 29 deposits, it is shown that the Ag/Au ratios differ in the ore bodies of volcanic and volcano-plutonic types.  相似文献   

Ore-finding method of fault tectono-geochemistry in the Tongchang Cu-Au polymetallic orefield, Shaanxi, China： I. Dynamics of tectonic oreforming processes and prognosis of concealed ores   总被引：3，自引：2，他引：1  

Runsheng Han  Deyun Ma  Peng Wu  Gengsheng Ma 《中国地球化学学报》2009,28(4):397-404

Based on the research content and conception of dynamics of tectonic ore-forming processes, with the focus on the dynamics and processes of mineral source, ore formation, transport, accumulation, dissipation and mineralization in response to magmatic invasion and metallogenic fluid under tectonic stress, this paper deals with the ore-finding method of fault tectono-geochemistry and its application on the basis of ore deposit genesis, “giant pressure shadow” structure and ore-finding method of tectonic stress field in the Tongchang orefield, expounds the rules of magmatic emplacement and ore fluid migration and concentration under the control of the structural stress field, hence providing the theoretical basis for the localization and prognosis of concealed ores. The fault tectono-geochemical features show that the Cu-Au polymetallic ore deposits (mineralization) in the orefield are closely related with volcano-(exhalation) sedimentation, magmatism and tectono-reworking. Fault tectono-geochemical anomalies can be applied to prognosis of metallogenetic target areas for ore exploration and can provide strong evidence of “giant pressure shadow” structure. In addition, quite a number of important target areas have been defined in combination with the characteristics of the tectonic stress field, and part of the target areas have been proved by practical activities.  相似文献   

福建浦城上厂矿田铜钼多金属矿成矿预测研究     

卢克标 《福建地质》2009,28(1):10-20

根据蚀变分带及矿物组合、矿田地球化学分带及元素组合特征,对矿床类型及成矿模型特征进行探讨。成岩与成矿作用在时空上总体具有由西南向东北迁移演化的特点,上厂矿段为中高温Mo（Cu、Pb、Zn）矿→金竹坑矿段为中低温Cu、Pb、Zn（Ag）矿→雷母寨矿段为中低温Ag、Pb、Zn矿。三者从时间、空间、物源等方面有依存关系,以及矿化类型专属性等,可以将矿田矿床划分斑岩型铜钼多金属矿床及火山-次火山热液型铅锌银多金属矿床2个成矿类型,并类比预测矿田矿化类型及找矿方向。  相似文献   

福建浦城双坑铅锌银矿区地质地球化学特征及找矿方向     

李南生 《福建地质》2009,28(3):205-212

双坑矿区位于浦城管查-建阳溪东铜多金属找矿远景区内,水系沉积物和土壤金属量测量异常规模大,套合好、峰值高,具明显的浓集中心。区内分布有铅锌银丰度值高的大金山组变质岩和燕山早期黑云母花岗岩,断裂裂隙发育,成矿地质条件有利。通过区域地质条件、异常元素组合与分布特征分析,探讨矿区找矿方向。  相似文献   

小秦岭地区（陕西部分）钛矿找矿方向及工作方法     

李六权 《陕西地质》2009,27(2):12-20

小秦岭地区具有寻找变质岩型等钛矿的地质条件,并已发现有多处金红石、钛铁矿线索。研究认为,小秦岭地区中元古界熊耳群及高山河组地层为寻找变质岩型钛矿有利层位,洛南西沟是碱性岩型钛矿成矿有利区;洛南石门-瓦子坪地区、兰田坝塬-洛南洛源地区和洛南白楼-西沟地区等3个钛矿找矿远景区;石门盆地深部存在一个变质喷发岩型钛铁矿床。应运用重砂测量、高精度重力测量、高精度磁法和电法测量等工作方法开展普查,强化深部钻探找矿,将获得可喜的找矿成果。  相似文献   

豫西骆驼山硫多金属矿床的成因——来自纹层状矿石中硫化物LA-ICP-MS微量元素证据   总被引：1，自引：1，他引：0  

邢波  向君峰  叶会寿  陈小丹  张国苏  杨晨英  金雪  胡志中 《矿床地质》2017,36(1):83-106

骆驼山硫多金属矿床位于豫西栾川钼多金属矿集区,矿体主要呈似层状和透镜状产于新元古界栾川群三川组和南泥湖组的层间断裂带内的矽卡岩中,受NWW向层间断裂带的控制。该矿床在成因方面的争论的焦点在于:是否存在元古代的喷流沉积成矿作用?具有纹层状构造的硫化物矿石以往被认为是喷流沉积成因矿床的关键证据,但这种矿石结构也可能为热液交代成因。通过详细的野外地质观察,纹层状矿石在空间上主要产于矽卡岩与致密块状硫化物矿石之间,在透辉石长英角岩、矽卡岩及大理岩等围岩中也有分布,纹层状矿石交代了矽卡岩。针对纹层状矿石中的金属硫化物开展LA-ICP-MS原位微区分析,结果表明:(1)闪锌矿形成于中高温环境,其微量元素以富Fe、Mn、In、Co(均值分别为8.5%、6144×10~(-6)、321×10~(-6)和28.54×10~(-6)),贫Ga、Ge、Tl(均值分别为4.31×10~(-6)、0.98×10~(-6)和0.0476×10~(-6))等元素为特征;(2)磁黄铁矿和黄铁矿的微量元素组成均具有富Co(均值分别为57.75×10~(-6)和2787.68×10~(-6))、贫Ni(均值分别为19.24×10~(-6)和11.29×10~(-6))的特征,二者的Ni-Co关系图指示其与岩浆热液密切相关。以地质现象为基础,结合硫化物原位微区分析数据,笔者认为骆驼山硫多金属矿床中的纹层状矿石属于岩浆热液成因。  相似文献   

福建清流仁场铅锌银矿找矿方向分析     

罗锦昌 《福建地质》2004,23(3):119-123

清流仁场铅锌银矿是受推覆构造和层位双重控制的热液矿床．已控制矿体的赋存位置有明显的规律性,大致分布于“S”形的中部破碎带较厚的部位．由于断裂面产状变化引起的局部张性环境有利于热液交代和充填所致。根据这一观点,相应的构造位置就是今后的找矿靶区。  相似文献   

Fractal properties of multi-order folding as a tool for exploration of low-grade banded iron ores in the Krivoy Rog basin (Ukraine)     

D. A. Kulik  M. I. Chernovsky 《International Journal of Earth Sciences》1996,85(1):3-11

The low-grade Palaeoproterozoic stratabound banded iron ores of the Krivoy Rog basin (Ukraine) underwent strong tectonometamorphic deformation into superimposed folds of several orders, with amplitudes from centimetres to hundreds of metres. The across-strike sections of bed surfaces defining the low-grade ore bodies resemble self-similar fractal curves; hence, a fractal geometrical model was developed in order to quantify the complexity and sinuosity of bed contours. Two different methods of measurement (polygonal approximation and two-dimensional grid cell counting) were used for 5–8 different scales. Factual similarity dimension D and other model parameters have been estimated by means of linear regression and compared for both measurement methods. From the fractal model a sinuosity coefficient of contours of the folded bed surfaces K _s and a coefficient of degree of exploration of iron ore bodies K _e were constructed. It is pointed out that parameters of the model can be used for determination of the optimal exploration length scales.  相似文献