锡在地球中初始富集与锡矿床成矿关系

长期以来,地质学家们比较一致地认为锡矿床与花岗岩在成因方面有着密切的联系。近15年来,有些学者试图论证层控锡矿床的存在和意义。本文提出同生作用很难生成工业性锡矿床,但由其所形成的初始富集在诸多成矿区、带中普遍存在。这里所谓的初始富集与前人提出的矿源层概念不同,它包括以下三种不同的存在形式:第一、Sn 在地球中分布表现为不均一性。在 Sn 的高地球化学异常区、带内,各种地质体都具有高于同类岩石克拉克值一至数倍,乃至数十倍。这正是锡矿成矿的物质基础。第二、海底喷气作用导致 Sn 在高地球化学异常区、带内某些地区的某些层位初始富集或作为副产品存在于贱金属硫化物矿床中。第三、在地质历史中所形成的古砂锡富集体和矿点。上述三种 Sn 的初始富集,虽然不具工业意义,但一旦在适宜的地壳运动期间,其本身重熔成含锡花岗岩或受与花岗岩有关锡矿体的叠加或改造,即可成矿。Sn 的初始富集往往是形成超大型矿床的基本条件之一。

Petrology,genesis and geodynamic implication of the Mesoproterozoic-Late Cretaceous Timmasamudram kimberlite cluster,Wajrakarur field,Eastern Dharwar Craton,southern India

New mineralogical and bulk-rock geochemical data for the recently recognised Mesoproterozoic （ca. 1100 Ma） and late Cretaceous （ca. 90 Ma） kimberlites in the Timmasamudram cluster （TKC） of the Wajrakarur kimberlite field （WKF）, Eastern Dbarwar Craton, southern India, are presented. On the basis of groundmass mineral chemistry （phlogopite, spinel, perovskite and clinopyroxene）, bulk-rock chem- istry （SiO2, K20, low TiO2, Ba/Nb and La/Sm）, and perovskite Nd isotopic compositions, the TI（-1 （mac- rocrystic variety） and TI（-4 （Macrocrystic variety） kimberlites in this cluster are here classified as orangeites （i.e. Group II kimberlites）, with geochemical characteristics that are very similar to orangeites previously described from the Bastar Craton in central India, as well as the Kaapvaal Craton in South Africa. The remaining kimberlites （e.g., TK-2, TK-3 and the TK-1 microcrystic variant）, are more similar to other 1100 Ma, Group l-type kimberlites of the Eastern Dharwar Craton, as well as the typical Group I kimberlites of the Kaapvaal Craton. Through the application of geochemical modelling, based on pub- lished carbonated peridotite/melt trace element partition coefficients, we show that the generation of the TI（C kimberlites and the orangeites results from low degrees of partial melting of a metasomatised, carbonated peridotite. Depleted mantle （TDM） Nd perovskite model ages of the 1100 Ma Timmasamudram kimberlites show that the metasomatic enrichment of their source regions are broadly similar to that of the Meso- proterozoic kimberlites of the EDC. The younger, late Cretaceous （ca. 90 Ma） TI（-1 （macrocrystic variant） and TK-4 kimberlites, as well as the orangeites from the 8astar Craton, share similar Nd model ages of 1100 Ma, consistent with a similarity in the timing of source enrichment during the amalgamation of Rodinia supercontinent. The presence of late Cretaceous diamondiferous orangeite activity, presumably related to the location of the Marion hotspot in southern India at the time, suggests that thick lithosphere was preserved, at least locally, up to the late Cretaceous, and was not entirely destroyed during the breakup of Gondwana, as inferred by some recent geophvsical models.

Rift-associated ultramafic lamprophyre(damtjernite) from the middle part of the Lower Cretaceous(125 Ma) succession of Kutch,northwestern India: Tectonomagmatic implications

Mineralogical,geochemical and isotopic(Sr and Nd) studies on the recently reported ca. 124 Ma'anorogenic lamproite' dyke from the Palanpur area, Kutch seismogenic rift zone, northwestern India, are presented. We propose a new classification for the dyke as a damtjernite(ultramafic lamprophyre; UML)based on its porphyritic-panidiomorphic texture, abundance of phlogopite, presence of nepheline in the groundmass, and the composition of liquidus phases such as olivine, phlogopite, magnetite, and clinopyroxene(diopside). The Palanpur UML is primitive(Mg# =74-77),silica-undersaturated(SiO_2<40 wt.%),potassic to slightly sodic in nature, and is strikingly similar to the ～69 Ma UML dykes and sills of the Tethyan Indus suture zone, which are considered as the earliest yet known manifestations of the Deccan Large Igneous Province(LIP). Bulk-rock(^(87)Sr/^(86)Sr)_i(0.70460-0.70461) and ε_(N)d(t)(+2.56 to-0.69) of the Palanpur UML signify derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB. This is further attested to by the high incompatible trace element ratios(viz., La/Ba, Nb/U, Nb/La and Ta/Yb) that are typical of plume-type magmas. However, the Neoproterozoic T_(DM) depleted mantle Nd model ages( ～655-919 Ma) also necessitate some involvement of a lithospheric mantle component in its genesis. High bulk-rock Fe_2 O_3~t and TiO_2 contents require the involvement of a fertile peridotitic mantle source, whereas high La/Yb(60-80) implies a control by residual garnet. Higher Rb/Sr and lower Ba/Rb suggest phlogopite as a residual phase and high Nb and lower La/Sm favour carbonatite, rather than silicate melt as metasomatising agent. Low degrees of partial melting of a primitive garnet lherzolite mantle can account for the observed REE patterns in the Palanpur UML. The Palanpur UML shares a temporal similarity to the Kerguelen plume-derived Rajmahal basalts and associated alkaline rocks from the eastern India. The tectonomagmatic significance of its emplacement during the mid-Cretaceous vis-a-vis various models involving the timing of eruption of the Deccan and the Rahmahal Traps and the rifting in the Kutch basin induced by far-field plate reorganization is evaluated.

Zircon chemistry and new laser ablation U–Pb ages for uraniferous granitoids in SW Cameroon

The Ekomedion two-mica granite,southwestern Cameroon,has potential for uranium and molybdenum mineralization.Here,we present LA-ICP-MS U-Pb ages,Lu-Hf isotope characteristics,trace element concentrations and Ti-geothermometry of zircon from this granite hosting U-Mo mineralization in pegmatitic pods.The majority of zircon are CL-dark though some CL-bright cores were also identified.U-Pb zircon age data range from 121±3 to743±11 Ma with only 5 of 34 ages being near concordant.The concordant mean age of 603±12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon.Apparent ages with mean of261±6 Ma reveal open system behavior with respect to Pb and/or U.Zircon e Hfi values range from-20.3 to-0.3.This implies that U-Mo was remobilized during partial melting of the surrounding gneiss.Zircon Th/U>0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U-Mo mineralization in pegmatitic pods.Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization.Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U-Mo mineralization as a ligand.Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase.Calculated Ti-in-zircon temperatures span 672℃to1232℃with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.

立达公司:提高矩形条筒容条量的新概念

描述了德国立达(Rieter)公司提出的应用于RSB-D35的CUBIcan线上的矩形条筒新概念。介绍了这一新概念,内容包括:与传统的条筒相比,用于并条和随后的纺纱工序时其技术和经济方面的优势,通过优化升降装置的下降运动,可能带来的条筒容条量的增加。将来,这将有助于纺纱厂生产纱线时有效地利用条筒。

Petrogenesis of the crater-facies Tokapal kimberlite pipe,Indrvati Basin,Central India

New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic lndravati Basin a：：e presented. The kimberlite has been subjected to extensive and pervasive low-temperature alteration. Spinel is the only primary phase identifiable, while olivine macrocrysts and juvenile lapilli are largely pseudomorphed （talc-serpentine- carbonate alteration）. However, with the exception of the alkalies, major element oxides display systematic fractionation trends; likewise, HFSE patterns are well correlated and allow petrogenetic interpretation. Various crustal contamination indices such as （SiO2 ＋ AI：：O3 ~ Na20）]（MgO ~ K20） and Si] Mg are close to those of uncontaminated kimberlites. Similar La]Yb （＇79-109） of the Tokapal samples with those from the kimberlites of Wajrakarur （73-145） and Narayanpet （72-156）, Eastern Dharwar craton, southern India implies a similarity in their genesis. In the discriminant plots involving HFSE the Tokapal samples display strong affinities to Group 1I kimberlites from southern Africa and central India as well as to ＇transitional kimberlites＇ from the Eastern Dharwar craton, southern India, and those from the Prieska and Kuruman provinces of southern Africa. There is a striking ~;imilarity in the depleted-mantle （TOM） Nd model ages of the Tokapal kimberlite system, Bastar craton, th~ kimberlites from NKF and WKE Eastern Dharwar craton, and the Majhgawan diatreme, Bundelkhand craton, with the emplacement age of some of the lamproites from within and around the Palaeo^Mesoproterozoic Cuddapah basin, southern India. These similar ages imply a major tectonomagmatic event, possibly related to the break- up of the supercontinent of Columbia, at 1.3-1.5 Ga across the l：hree cratons. The ＇transitional＇ geochemical features displayed by many of the Mesoproterozoic po~：assic-ultrapotassic rocks, across these Indian cratons are inferred to be memories of the metasomatising fluids]melts imprinted on their source regions during this widespread event.