津巴布韦大岩墙北部红土型镍矿成矿条件及找矿标志

津巴布韦大岩墙北部红土型镍矿严格受橄榄岩控制,受地形地貌条件影响,位于橄榄岩出露的支谷山前缓坡地带的红土下部和靠山坡一侧.沟谷平坦和山上陡坡地段则无矿或有极薄氧化壳.该大岩墙上部橄榄岩、辉石岩、橄榄辉石岩带和铬铁矿层呈层状相互交替组成韵律性层序.在橄榄岩出露的地表植被稀疏,多为草本植物,而辉石岩、橄榄辉石岩带上呈现出茂密树丛.     

Contested diamond certification: Reconfiguring global and national interests in Zimbabwe’s Marange fields

This study examines the political uses of “conflict diamond” discourse in global debates about commodity certification and socially responsible mining in Zimbabwe. Engaging critical literature on “conflict-free” corporate branding initiatives, the study focuses on representations of conflict in Marange, in Zimbabwe’s eastern highlands. In 2006, a diamond rush in Marange drew in tens of thousands of artisanal miners from across Zimbabwe as well as foreigners, and the government initiated military crackdowns in 2008. In a highly contested vote in 2009, the international government delegates who comprised the voting members in the Kimberley Process Certification System (KPCS) ruled that conflict in Marange did not meet the KPCS definitions of “conflict diamond.” The study examines discourses of key stakeholders in the multinational diamond industry, human rights organizations, policymakers as well as artisanal miners in Zimbabwe between 2006 and 2014. The article argues that advocacies against diamond certification as well as advocacies favouring certification both tended to overlook the interests of artisanal miners, focusing narrowly on certain forms of conflict while associating artisanal mining with illicitness. The Marange case illustrates how conventional discourses on “conflict diamonds” not only obscure the complex nature of conflicts in contemporary capitalist accumulation processes; they also risk contributing to new forms of structural violence. This analysis highlights the need to pay careful attention to how global commodity certification discourses inter-relate with political agendas at multiple scales. The study draws attention to dilemmas for geographers when portraying the interests of marginalized groups in – and affected by – the diamond mining sector.     

Textural,mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke,Zimbabwe and the precious metals zone of the Sonju Lake Intrusion,Minnesota, USA

Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type.     

Integrating conventional classifiers with a GIS expert system to increase the accuracy of invasive species mapping

Mapping the cover of invasive species using remotely sensed data alone is challenging, because many invaders occur as mid-level canopy species or as subtle understorey species and therefore contribute little to the spectral signatures captured by passive remote sensing devices. In this study, two common non-parametric classifiers namely, the neural network and support vector machine were used to map four cover classes of the invasive shrub Lantana camara in a protected game reserve and the adjacent area under communal land management in Zimbabwe. These classifiers were each combined with a geographic information system (GIS) expert system, in order to test whether the new hybrid classifiers yielded significantly more accurate invasive species cover maps than the single classifiers. The neural network, when used on its own, mapped the cover of L. camara with an overall accuracy of 71% and a Kappa index of agreement of 0.61. When the neural network was combined with an expert system, the overall accuracy and Kappa index of agreement significantly increased to 83% and 0.77, respectively. Similarly, the support vector machine achieved an overall accuracy of 64% with a Kappa index of agreement of 0.52, whereas the hybrid support vector machine and expert system classifier achieved a significantly higher overall accuracy of 76% and a Kappa index of agreement of 0.67. These results suggest that integrating conventional image classifiers with an expert system increases the accuracy of invasive species mapping.     

津巴布韦匹克铬铁矿地质地球化学特征及矿床成因

匹克铬铁矿是津巴布韦少有的大型透镜状铬铁矿床之一。文章总结了匹克铬铁矿的成矿地质背景、矿床地质特征、矿床地球化学特征和矿床成因方面的研究进展。文章认为该矿床的初始组分与初始科马提岩型铬铁矿相似,主量元素表明铬铁矿的氧逸度比较低,保留了岩浆初始的还原环境,并表现出岩浆结晶分异演化的特征。尽管矿床形成之后受到交代和角闪岩相变质作用的影响,但初始组分没有被显著破坏。矿床所在地区铬铁矿Re-Os同位素分析表明,津巴布韦克拉通岩石圈地幔同位素比值显著低于硅酸盐地球的平均值,并没有受到上地幔对流的影响。归纳了前人对匹克铬铁矿成因的几种观点,提出矿床的成矿模式和形成过程。     

‘All my hopes and dreams are shattered’: Urbanization and migrancy in an imploding African economy - the case of Zimbabwe

During the 1990s, urban livelihoods in Zimbabwe began to suffer a series of economic stresses, which accelerated in 1997 and then accelerated again, with the inception of fast-track land reform, from 2000. This has reduced urban living standards significantly and devastated real urban income levels. After a discussion of the economic and political parameters of this period, this paper links these to empirical changes in the urban livelihoods and perceptions of urban living standards of recent in-migrants to Harare. This draws on a longitudinal database of four surveys of recent migrants to the city conducted in 1985, 1988, 1994 and 2001. Among a range of qualitative issues explored in these surveys has been the question of migrants’ future plans in relation to their intended length of stay in town. It is shown that migrants have been feeling increasingly negative or unsure about their urban experience since structural adjustment began in the early 1990s, and that these perceptions had greatly strengthened by 2001. By the last survey only a small minority felt they would remain permanently in town and most of the migrants from rural areas felt that their living standards in Harare were either worse than rural living standards, or no better. While Zimbabwe’s current political and economic crisis is exceptional, serious urban poverty is a feature across sub-Saharan African countries and it is argued that this has had a depressing effect on net rural-urban migration rates.     

Timing of thermal stabilization of the Zimbabwe Craton deduced from high-precision Rb–Sr chronology, Great Dyke

Dating low temperature events such as magmatic cooling or (hydro-)thermal surges in Archean and Proterozoic terranes is crucial in defining cratonal thermal stabilization after episodic continental growth during the Archean and Early Proterozoic. Rubidium–Sr chronology is potentially a powerful tool in this regard because of its low closure temperature, i.e., <400 °C in most minerals, but has until now been hampered by its relatively low precision compared to high-temperature chronometers. Consequently, Rb–Sr age investigations have so far failed to provide high-precision age constraints on the cooling of rocks older than 2 Ga. Here, it is demonstrated that internal Rb–Sr microchrons can yield important, high-precision age constraints on the cooling history of Archean intrusions. After careful mineral selection and chemical treatment, a Rb–Sr age of 2543.0 ± 4.4 Ma was obtained from the Archean Great Dyke, Zimbabwe Craton, in contrast to the intrusion age of 2575.8 ± 1 Ma, yielding an ambient average cooling of 5 ± 2 °C/Ma. The non-disturbed magmatic Rb–Sr cooling age of the Great Dyke marks the final stage of Zimbabwe craton stabilization and that the greater craton area did not experience any intensive later reheating event during metamorphic or tectonic events.     

Planning versus youth: Stamping out spatial unruliness in Harare

The paper examines the illegal occupation and use of urban spaces by Harare’s youth and the ensuing tussles with the repressive machinery of the local authority and the nation-state. It analyses efforts by planning to contain rampant spatial unruliness. The paper maps the patterns of official hostile responses to the illegal activities of the youth whose daily routines inevitably entail the disregard of the spatial planning framework as reflected in existing legal and regulatory controls. The analysis reveals the reliance by the urban planning and management system on the use of force and violence, a feat made possible by the mobilisation of the repressive state apparatus. The discussion argues that what comes out in the relationship between the order-imposing planning system and the regulation-flouting youth is a situation that can largely be comprehended by turning to the non-progressive side of planning.     

The hydrology of sand rivers in Zimbabwe and the use of remote sensing to assess their level of saturation

Sand rivers are ephemeral watercourses containing sand that are occasionally flooded with rainwater runoff during the rainy season. Although the riverbed appears dry for most of the year, there is perennial groundwater flow within the sand. This water flowing beneath the surface is a valuable resource for local communities; nonetheless our understanding of such river systems is limited. Hence, this paper aims to improve our understanding of the hydrology of sand rivers and to examine the potential use of remote sensing to detect the presence of water in the sand. The relationship between rainfall events and changes in the water level of two sand rivers in the Matabeleland South Province of Zimbabwe was investigated. A lagged relationship was observed for the Manzamnyama River but for the Shashani River the relationship was seen only when considering cumulative rainfall events. The comparison of the modelled flow as simulated by a water balance model with observations revealed the important influence of the effective sediment depth on the recharge and recession of the alluvial channels in addition to the length of the channel. The possibility of detecting water in the alluvial sands was investigated using remote sensing. During the wet season, optical images showed that the presence of water on the riverbed was associated with a smooth signal, as it tends to reflect the incident radiation. A chronological analysis of radar images for different months of the year demonstrates that it is possible to detect the presence of water in the sand rivers. These results are a first step towards the development of a methodology that would aim to use remote sensing to help reducing survey costs by guiding exploratory activities to areas showing signs of water abstraction potential.     

津巴布韦东部Mutema地区地球化学特征及成矿预测

根据津巴布韦东部地区1∶25万区域地球化学调查成果,运用地质、化探、遥感等对该地区进行了地球化学特征、成矿规律研究和找矿预测,确立了以金为主的Tarka地区和以Ni,Cu为主的Limeworks,Mutema地区为找矿靶区;认为Tarka地区金矿并非粗玄岩次生富集而成,而是受构造控制并与热液活动引起的金活化富集有关;中部的高镍异常区是寻找红土型镍矿的有利部位。