共查询到20条相似文献，搜索用时 15 毫秒
1.
Dave Craw 《Mineralium Deposita》2013,48(7):841-860
Many alluvial placer deposits around the world occur in river systems that have been affected by tectonic events, causing drainage reorientation and severance of links between placers and their sources. This study documents tectonic rejuvenation of topography in the Otago giant placer goldfield, New Zealand, which has resulted in numerous river capture and drainage reorientation events. These events have induced changes to gold transport directions and numerous stages of separation of detrital gold from primary sources. Goldfield-wide reconstructions of drainage patterns through time are as yet only possible for Miocene–Recent, and numerous earlier drainage changes back to Cretaceous primary orogenic mineralisation are probable. Variations in basement lithologies permit auriferous gravel provenance determinations, facilitating paleodrainage pattern reconstruction and documentation of river capture events. River capture events and timing of these events for gold-bearing paleodrainages have also been documented using genetic divergences of populations of freshwater galaxiid fish that were isolated by drainage reorientation. Gold-bearing quartz pebble conglomerates had a southeastward drainage in the Miocene. This was disrupted in the Pliocene by mountain range uplift and gold placer recycling, with deposition of lithic conglomerates containing only minor gold placers. The most dramatic changes in gold transport directions occurred through the Quaternary, as antiformal ranges grew across the pre-existing drainages. Miocene and Pliocene placers were recycled with numerous local (1–10 km scale) changes in river directions and numerous capture events. Large axial rivers were segmented into a more complex drainage pattern, and on-going river capture resulted in growth of the main Clutha River catchment at the expense of neighbouring catchments. The most productive placers developed in the Clutha River in late Quaternary when increased discharge from captured mountain catchments enhanced gold transport and concentration. Similar river drainage reorientation has occurred in other placer fields around the world, but the lack of preserved evidence inhibits documentation of most such changes. 相似文献
2.
Yu. I. Goldfarb 《Geology of Ore Deposits》2007,49(4):241-270
The comprehensive study of alluvial gold placers, fluvial sediments, and river valleys allowed division of these placers into subtypes, categories, and varieties on the basis of genetic principles. The comparison of observation results with reconstructions of placer-forming fluvial processes demonstrates the distinct dependence of all basic properties of placers on the dynamics of their formation, i.e., on the hydraulic size of gold grains, the dimensions of streams, and the phase of the elementary erosion cycle (PEC). Four PECs are distinguished: erosion, abrasion, equilibrium, and aggradation. A lithodynamic alluvial complex (LDAC) of the same name corresponds to each PEC. Any fractions of free gold can be transported by streams, and the mode of transportation depends on the PEC. Placers of eight dynamic categories, brush, erosion, perluvial, apron, bar, equilibrium, aggradational, and gravitational, are syngenetic to certain lithofacies belonging to different LDACs. The first four categories are combined into the channel-line subtype, which embraces all traditional placers. The nontraditional bar and equilibrium (beach subtype) and aggradational and gravitational categories (representing two subtypes of the same name (?)) are so far poorly studied but may be regarded as highly promising. The size, morphology, thickness, structure, and localization of placers; average and modal values of size and roundness of gold grains; degree of their sorting and concentration; three-dimensional distribution of gold; composition of alluvium; relationships of placers with alluvium and the gutter, river valleys of various sizes, and types of morphostructures; and other features are distinct for placers pertaining to specific categories and make up natural groups individualized for each category. The correlation of placer properties in each category makes these properties predictable at the early stages of geological exploration and enhances the efficiency of forecasting and prospecting. In high-grade gold clusters, closely spaced placers group into composite deposits. The subdivision of these placers into categories makes it possible to apply rational methods and tools of exploration and mining of placers; to estimate the character, volume, and location of previous losses of gold; and to select targets for their remining. The dynamic analysis of recently formed and ancient placers is helpful for implementation of panning and interpretation of the results obtained in the context of prospecting for gold. The proposed classification may be used not only in the study of stream gold but also in the exploration of some other placer deposits. 相似文献
3.
N.A. Roslyakov M.V. Kirillov N.S. Morozova S.M. Zhmodik Yu.A. Kalinin G.V. Nesterenko N.V. Roslyakova D.K. Belyanin V.V. Kolpakov 《Russian Geology and Geophysics》2013,54(5):483-494
Holocene shallow (0.5–4.5 m, rarely more) and Pliocene–Pleistocene deep (> 25 m) placers occur within the China tectonic depression. The shallow placers are associated with the formation of the present-day drainage valleys of the China River under permafrost conditions, and the deep ones are localized within the preglacial paleovalleys of the river basin. An integrated geological and geochemical study was carried out at ten shallow commercial placers, eight of which are classified as poorly studied and “unconventional.” Placers are considered “unconventional” based on their technological characteristics (commercial gold is small (? 0.25 to + 0.1 mm), thin (? 0.1 mm), and micron-sized or “bound” (invisible)), geomorphologic conditions of formation, confinement to the oxidized zone of active permafrost, significant portion of fine hydrogenic gold, and several other minor features.The formation of shallow “unconventional” placers is controlled by the conditions of active permafrost. Under aerobic conditions, suprapermafrost waters form an oxidized zone, in which iron hydroxides impart a yellowish reddish color to water-bearing rocks. Long-lived geochemical barriers (biogenic, reduction, electrochemical, sorption, and others), including gravitational differentiation, play an important role in the concentration of small and thin gold.Alluvial deposits in Meso-Cenozoic tectonic depressions, such as the China basin, are the most promising in terms of “unconventional” placers. The main factors favoring the formation of these localities and the criteria for their assessment are large feeding sources of gold (mainly carbonaceous and sulfide) mineralization, endogenic and exogenic dispersion aureoles with thin and invisible gold; increased thickness of the suprapermafrost active layer and its temporal and spatial stability, contributing to the formation and functioning of oxidized horizons with the accumulation of ferric hydroxide and hydrogenic gold; specific morphologic varieties of hydrogenic gold, which are the fundamental criterion for primary gold mineralization with migratable metal; fine-clastic clay-rich composition of recent alluvial or alluvial-talus sediments, produced by water reworking of ancient gold-bearing weathering crusts; and development of broad floodplains filled with Holocene sediments and their junction with talus-solifluction erosional slopes. 相似文献
4.
I.S. Litvinenko 《Russian Geology and Geophysics》2012,53(7):657-668
We consider the formation of the Dal’nii (Dal’nyaya) eluvial gold placer (Bol’shoi Anyui ore–placer district, western Chukchi Peninsula), related to the Dal’nii (Dal’nee) gold-bearing porphyry Mo–Cu occurrence. The Dal’nii placer is located within the transition between the Kur’ya Ridge and Anyui basin, which has been relatively stable at the recent (Pliocene–Quaternary) tectonic stage. Minor recent uplift has determined the slight denudation of interfluves, the leading role of eluvial processes in the formation of a loose cover on them, and the preservation of the relict matter of pre-Pliocene chemical-weathering crusts (including the oxidized zones of orebodies) in present-day eluvium. The Dal’nii placer consists of relict weathering-crust placers altered by recent eluvial processes in different degrees. Therefore, it is relatively rich in metal, whereas the primary lode contains mainly fine-sized gold, which is almost not released from ore under periglacial lithogenesis in present-day interfluves. We suggest calling this genetic type of placers “residual-eluvial.” The primary lodes being highly eroded (during the formation of residual concentrations, which serve as an intermediate reservoir for these placers), residual-eluvial placers or their parts might not be directly related to specific orebodies at the present-day level of erosional truncation. 相似文献
5.
Typomorphic features of placer gold in the eastern Siberian Platform were studied to determine its genesis. It was established
that this region contains abundant alluvial bar placers, which were formed mainly by the erosion of gold reservoirs of different
ages. Discovery of gold with the points of eolian reworking in the Quaternary sediments allows us to predict the eolian gold
placers in individual areas of the northeastern and central parts of the eastern Siberian Platform. Identification of two
types of gold on the basis of typomorphic features in the Cenozoic deposits indicates that placer gold was mainly derived
from the Precambrian sources spatially confined to the exposure of ancient basement, as well as from local ore occurrences
related to the Mesozoic tectonomagmatic activation. Thus, two main stages of ore formation (Precambrian and Mesozoic), were
substantiated for the first time in the eastern Siberian Platform. 相似文献
6.
ALLUVIAL STYLES AND ARCHITECTURE AS GUIDES TO CENOZOIC TECTONIC AND ENVIRONMENTAL EVENTS AT THE NORTHERN MARGINS OF THE QINGHAI—XIZANG PLATEAU 相似文献
7.
Numerous auriferous fluvial quartz pebble conglomerates (QPCs) are present within the Late Cretaceous–Recent sedimentary sequence in southern New Zealand. The QPCs formed in low-relief settings before, during, and after regional marine transgression, in alluvial fan and a variety of fluvial and near-shore depositional settings: In particular, during slow thermal subsidence associated with Late Cretaceous–early Cenozoic rifting, and during the early stages of orogenic uplift following mid Cenozoic marine regression. QPC maturity characteristics are complex and vary with sediment transport and recycling history, stratigraphic proximity to the transgressive Waipounamu Erosion Surface, and the amount of first-cycle detritus incorporated during recycling. For pre-marine QPCs, the amount of first cycle detritus varies with tectonic intensity and proximity of the depositional setting to remnant Cretaceous topography. For post-marine QPCs, it varies with tectonic intensity and proximity to Late Cenozoic uplift of basement ranges.QPCs do not form during a single bedrock erosion–sediment deposition cycle: Non-oxidised and/or oxidized groundwater alteration (kaolinisation) of labile minerals in immature sediment and the upper part of underlying basement, and repeated sedimentary recycling, are fundamental processes of QPC formation regardless of the tectonic or sedimentary settings. Altered immature rock disaggregates easily upon erosion, and alteration clays are winnowed to leave quartz-rich residues containing resistant heavy minerals such as zircon and gold. Detrital sulfide survives recycling if deposition and burial in saturated sediments are rapid. QPCs result only if sediment recycling is not accompanied by excessive erosion of fresh basement rock. Uplift of many parts of the Otago Schist belt since late Miocene has raised rocks above the water table, increased erosion rates, and inhibited groundwater alteration and QPC formation. QPC formation is still occurring in Southland, where the water table is high, sediments are saturated and undergoing alteration, and uplift and erosion rates, topography, and fluvial gradients are all low. The QPCs accumulate as residual gravel on the valley floors of low-competence streams that are slowly incising pervasively altered dominantly late Miocene–Pliocene immature conglomerates.QPCs formation essentially represents physical and chemical lagging of precursor strata. Accumulation of detrital gold and other heavy minerals is an inevitable consequence, and most QPCs contain some gold. Three types of significant gold placer have developed in the QPCs. Type 1 placers are essentially eluvial and/or colluvial in origin and form without significant fluvial transport, by residual accumulation in low-competence valleys during low-rate uplift, fluvial incision and QPC formation. Type 2 placers have formed during significant fluvial transport and subsequent fluvial incision, mainly in higher energy proximal and medial reaches of larger pre-marine (Eocene) and post-marine fluvial systems. Type 3 placers formed by wave-base and marine current winnowing in the shallow shelf setting during low-rate regional marine transgression, especially in the Eocene. 相似文献
8.
《Russian Geology and Geophysics》2007,48(10):783-798
This paper deals with the behavior of fine gold particles (0.25–0.1 mm) and gold dust (<0.1 mm) during the formation of alluvial placers in denudation areas in southern West Siberia. Native gold particles with a low settling velocity, <5–10 cm/s, such as dust (<0.1 mm) and fine flat particles, are transported with a river stream beyond denudation areas. This easily migrating gold participates in the formation of lithochemical flows, which are an important indicator of gold mineralization. It occurs in the upper beds of alluvial section. Heavier fine gold particles are partly retained at the site of river activity, and the rest are partly redeposited in cooler parts of placers, being graded according to their settling velocity, as evidenced from the direct relationship between the flatness and size of gold particles. Fine gold particles do not form large accumulations in alluvial autochthonous placers. The main typomorphic features of fine gold particles and gold dust are their abundance in ore sources, compositional similarity to larger gold fractions, and high migration ability. In contrast to morphological features of gold, these ones remain stable during the river drift. 相似文献
9.
G. V. Nesterenko N. A. Roslyakov S. M. Zhmodik Yu. A. Kalinin N. S. Morozova M. V. Kirillov V. V. Kolpakov D. K. Belyanin S. R. Osintsev 《Lithology and Mineral Resources》2014,49(1):29-46
Study of gold potential of the Late Cenozoic alluvium in the Bauntov area is based on the Taloi basin and Sivo sector (China River basin). Primary placer-forming gold is mainly represented by endogenous varieties. In contrast to alluvium of streams in the Taloi basin, Middle-Upper Quaternary alluvium of the Sivo sector (China River basin) is enriched in fine and tiny gold (smaller than 0.25 mm). The paper presents data testifying to a low Au content in the silt fraction of slimes from boreholes drilled in the Cenozoic alluvium (alluvium-deluvium) from transverse valleys in the Taloi basin and, hence, to an significant manifestation of the chemogenic concentration of this metal therein. Issue of the existence of specific conditions favorable for the formation of hydrogenic gold in the northern high-latitude zones requires further studies. The results show that lithochemical gold aureoles have an important prospecting significance. They also suggest the practical significance of accumulations of fine and tiny gold in the syn-stratal alluvium and alluvium-deluvium of large ore placer areas. 相似文献
10.
Centuries of intense mining of noble metals from placers of the southern Far East has exhausted their reserves. The prospects for increasing the raw material base of the region are connected with complex exogenic deposits, where noble metals play a subordinate role. The study of native gold from Ti-bearing placers spatially and genetically associated with the Ariadna mafic-ultramafic massif located on the right side of the Bol’shaya Ussurka River reveals the placer-forming role of polygenic and polychronous bedrock sources. Mafic-ultramafic rocks yielded cupriferous and mercuric gold; quartz veins with Au-As mineralization likely serve as another source of placers. 相似文献
11.
Typomorphic features of native gold and its contents in complex Ti–Zr placers in the southern West Siberian Plain are reported. Three of the placers are of littoral-marine genesis, and two formed under conditions of an alluvial piedmont plain. Native gold from the studied Ti–Zr placers occurs mainly as flattened thin (?0.1 mm) particles which underwent mechanical action. It is marked by wide fineness variation and the abundance of a very fine (990–1000‰) variety. Most likely, this is chemically transformed clastogenic metal. The gold content of the productive bed (5–30 mg/m3 native gold and 8–140 ppb bulk gold) is consistent with the dispersion of heavy ore and accessory minerals during mechanical migration in water flows simultaneously with their concentration on geochemical barriers. The native-gold content of complex Ti–Zr placers shows a higher negative correlation with the primary source–placer distance than those of Ti and Zr minerals and a positive correlation with the degree of hydrodynamic reworking (gravity concentration) of transit terrigenous material. On the southern framing of the West Siberian Plain, some regions of northern Kazakhstan are promising for gold of complex Ti–Zr placers as well as fine- and thin-gold placers, gold-bearing weathering crusts, and primary gold deposits. 相似文献
12.
13.
云南曲靖盆地构造演化及其对生物气成藏条件的控制 总被引：1，自引：0，他引：1
曲靖盆地是在云南省发现的具有工业价值生物气藏的第三系沉积盆地之一。利用二维地震测线结合地质和钻井等资料开展了详细的构造和沉积解释,对曲靖盆地的构造特征、盆地形成和演化进行了较为系统的综合研究,分析了构造演化对生物气成藏条件的控制作用。曲靖盆地的早—中渐新世的断陷阶段为大套湖相暗色泥岩(蔡家冲组)形成时期;渐新世晚期—上新世早期为盆地整体抬升萎缩阶段,避免了蔡家冲组有机质的大量消耗,保存了第四纪以来生物气成藏的有机物质;晚上新世的盆地坳陷阶段为茨营组含煤层系(次要气源岩)、储集层、盖层和岩性圈闭形成的主要时期;上新世末的压扭抬升萎缩阶段是断背斜和断鼻等构造圈闭和构造—岩性复合圈闭发育时期;第四纪盆地稳定沉降阶段为生物气聚集成藏时期。 相似文献
14.
青藏高原东北缘西秦岭北缘构造带的漳县地区出露一套具有磨拉石沉积特征的上新统韩家沟砾岩。其现今的空间分布和沉积特征对于认识青藏高原东北缘新生代构造演化和地壳隆升具有重要的科学意义。通过对上新统韩家沟砾岩层的厚度、砾石成分、形态和粒度特征、古流向特征、物源特征等研究,探讨其沉积环境和形成的构造背景。提出了西秦岭北缘上新统韩家沟砾岩代表新近纪上新世以来,西秦岭地块向北逆冲推覆构造背景下形成前陆磨拉石盆地沉积的认识。该区域上新统韩家沟砾岩现今出露最高高程与北缘断裂带之南的山顶夷平面高程相近,可能指示了其形成之后和西秦岭一起经历了长期的侵蚀夷平,最后在新近纪末期或第四纪初形成了统一夷平面。该夷平面代表了青藏高原东北缘地壳隆升的起点,新近纪末期以来,该夷平面的隆升、侵蚀和解体记录了青藏高原东北缘地壳隆升过程,即青藏高原东北缘真正隆升是新近纪末期或第四纪以来的地质事件。 相似文献
15.
该区具有重要工业意义的砂金矿床,几乎皆是流水成因的。研究其矿质来源、含金地质体的风化剥蚀作用、砂金矿在河谷中的搬运方式和距离、砂金矿的成矿作用及矿床特征,不但可以扩大砂金矿的找矿前景,还能为在砂金矿分布区寻找岩金矿提供依据。 相似文献
16.
帕米尔东北缘地区构造变形特征与盆山结构 总被引：7，自引：0，他引：7
帕米尔东北缘乌泊尔地区是正确认识帕米尔北缘盆山结构和构造变形特征非常关键的地区,本文利用连续电磁剖面(CEMP)资料和地震资料,并结合野外地质调查资料和钻井资料,对帕米尔东北缘乌泊尔地区的盆山结构和构造变形特征进行了研究。认为帕米尔东北缘及其以北地区的盆山结构表现为帕米尔造山带向北冲断和南天山向南冲断所形成的对冲结构;帕米尔山前为基底卷入式构造,古生界—中生界沿高角度的逆冲断层推覆到新近系和第四系之上,形成山前的古生界—中生界逆冲推覆带;北侧由受乌泊尔断裂控制的深部隐伏冲断体系和浅部的第四纪背驮盆地所构成。研究区的新生代构造变形时间开始于上新世晚期,并持续变形至今,形成了下更新统西域组(Q_1x)与下伏上新统、Q_2与Q_1和Q_(3-4)与Q_2之间的不整合。研究区最小构造缩短量为48.6 km,缩短率为48.1%。 相似文献
17.
长江口区晚新生代沉积物粒度特征和沉积地貌环境演变 总被引：7，自引：0，他引：7
对长江河口区的三个晚新生代钻孔作了地层对比和粒度分析,据此探讨晚新生代长江河口的沉积地貌环境演变过程。结果表明,SG6和J18A孔上新世厚层含砾砂质沉积物粒度特征,反映了洪积扇和冲积扇相沉积环境,沉积物搬运距离短;而SG13孔缺失上新世沉积,反映古地势较高,以剥蚀为主。因此上新世长江三角洲地区古地势高差较大,侵蚀区和沉积区共存。早更新世,本区继承了上新世的冲、洪积扇沉积环境,但SG6孔泥质沉积明显变厚,J18A孔此时则以厚层含砾砂沉积为主,SG13孔也开始接受泥质沉积,反映在构造沉降作用下,冲、洪积扇体向西、南部迁移,沉积盆地范围扩大。中更新世,沉积物普遍变细且以悬浮沉积为主,显示了曲流河或曲流河冲积平原的沉积环境。晚更新世初,本区又发育含砾砂层,特别是SG13孔出现厚层含砾砂,但是粒径显著小于上新世和早更新世沉积物,反映本区再次发生显著构造沉积,河流地貌广泛发育。晚更新世中晚期和全新世沉积物以粘土和粉砂质粘土为主,悬浮沉积占优,说明本区已演变为滨、浅海沉积环境。因此在构造沉降、剥蚀和沉积的共同作用下,本区的地貌演变经历了自上新世至中更新世和自晚更新世至全新世的两次准平原化过程。 相似文献
18.
贵州“红土型”金矿成因类型新说 总被引：4，自引：1，他引：3
在贵州的西南部地区已探明了几处大、中型赋存于第四系松散堆积层中残坡积型金矿床,它具有分布广,规模大及品位较低和暴露地表易采选的特点。在邻近的云南、广西地区也有发现。在此之前,其成因类型被认为红土型金矿。根据最近的成矿区划,科研,勘查等资料证实,该类型金放是微细浸染型岩金矿床作为矿源地质体经近地表风化堆积形成。矿床具有特殊的风化,堆积、保存条件。矿体形态受下伏茅口组古今岩溶喀斯特形态的制约,金的含量 相似文献
19.
20.
渤海位于渤海湾新生代裂陷盆地中段的东部。最近用大量三维地震勘探资料对渤海第四系及其构造所做的精细解释和分析,发现地层内普遍存在4个不整合（角度和平行不整合）面,表明曾发生过4期构造活动。但因渤海缺少完整的第四系岩芯剖面,无法对其进行系统分层和断代,更无从确定构造活动的时间。为解决这一难题,文章基于渤海湾盆地阶段性沉降和其周围山地间歇性抬升的相关性,以及它们具有统一的形成机制和同一动力学过程的认识,通过研究盆地周围山地第四纪构造运动塑造的多级河流阶地,并结合火山活动研究资料,推测渤海第四系内4个不整合面形成的时间是900～400kaB·P·,100～80kaB·P·,50～40kaB·P·和10～8kaB·P·,即早更新世晚期-中更新世早期、晚更新世早期和中期、全新世早期。 相似文献