美国Culberson重晶石-硫磺矿中流体包裹体的研究

Culberson自然硫-重晶石矿床位于美国德克萨斯州的Delaware油气盆地中,是北美最大的自然硫矿床。它产在晚二叠世Ochoan期的Castile组和Salado组的石灰宕夹薄层蒸发岩和有机质灰岩中,重晶石和自然硫是后生的,常交代这两个组地层中的蒸发岩和富含有机质的灰岩,并填充在古喀斯特中。流体包裹体的研究表明：有两个世代的包裹体,即成岩时和方解石后生加大和重晶石中捕获的石油包裹体和流体包裹体。按包裹体的成分和相态可分为一相液体包裹体、二相气液体包裹体和油气包裹体。研究表明,在方解石、重晶石和天青石的同一生长带中可见到含有不同气液比的流体包裹体、空的包裹体和油气包裹体,它们是在一个不混溶的环境中捕获的,因而其均一温度的测定并不可靠。流体包裹体的T_e在-18℃～-24℃之间,属于NaCl- H_2O体系,盐度为2%～10%。有许多油气包裹体,因而其成矿流体应是一个温度小于100℃的油田水．     

Metallogeny of the Lannigou Sedimentary Rock-hosted Disseminated Gold Deposit in Southwestern Guizhou Province, China

The Lannigou deposit is a large-sized sedimentary rock-hosted disseminated gold （SRHDG） deposit located in the Youjiang Basin. It is hosted by the Middle Triassic turbidite. Wall rock alterations, including silicification, pyritization, arsenopyritization, carbonatization and argillization, commonly occur along fractures. PGE study demonstrates that either Permian basalts or Triassic ultrabasic intrnsives are unlikely to be the main source of gold mineralization. Coupled with the lack of other nmgmatic activity in the vicinity of the mining area, an amagmatic origin is proposed. Organic matter compositions and GC-MS analysis of the ores and host rocks show that the organics in the ores and the host rocks have a common source; the organic matter in the ores was mainly indigenous. The positive correlation between S2 and Au contents, along with the common occurrence of organic inclusions, suggest involvement of organic matter in the ore-forming process in terms of promoting Au leaching from the source rocks, making colloidal Au migration possible, as well as hydrocarbon reduction of sulphate. Geological and geochemical characteristics of the Lannigou deposit suggest that it was formed through circulation of meteoric water and probably less importantly organic bearing formation water driven by high geothermal gradient caused by late Yanshanian extension, which leached Au from the source bed, and then migrated as Au-bisnlfides and colloidal Au, culminating in deposition by reduction-adsorption and surface complexation of gold onto the growth surface of arsenlan pyrite.     

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 ¹⁴C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 ¹⁴C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 ¹⁴C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 ¹⁴C yr BP and 10,032 ± 40 ¹⁴C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.