Iron sulphide formation in an exhalative-sedimentary environment,Talasea, New Britain,P.N.G.

Concentrations of iron sulphide minerals in sediments within and adjacent to a small intertidal thermal pool near Talasea township are forming and being modified under a wide range of exhalative-sedimentary conditions. A geochemical, mineralogical and bacteriological investigation of these iron sulphides has defined the major reactions leading to their formation and indicated aspects in which their mineralogies, textures and mechanisms of formation differ significantly from those of iron sulphides formed under “normal” sedimentary conditions. The main features of the thermal pool environment are: 1. the occurrence of relatively high iron sulphide concentrations; 2. the preservation, by the strongly anaerobic thermal spring waters, of hydrotroilite formed in the thermal pool sediments in the presence of excess sulphide; 3. the presence in the pool banks of major marcasite (which appears to replace its dimorph pyrite) formed as a result of the development of strongly acidic conditions; 4. the abundance in the pool banks of large euhedral crystals of pyrite and marcasite, and the scarcity of framboids; 5. the presence of sulphate-reducing bacteria in the thermal waters and sediments.     

两个古铜辉石样品的G.P区研究

在两个斜方辉石样品中观察到G.P.区亚稳相。内蒙古暗色辉长岩古铜辉石成分是En_(77)Fs_(18·6)Wo_(4·4),其高分辨象显示了密集的单层G.P.区;玄武岩中变辉长岩包体古铜辉石成分是En_(72·2)Fs_(25·7)Wo_(2·1),具双层G.P.区。该包体与具多层G.P.区的月岩橄长岩相似,后期冷却极快。在地体火成岩体结晶和冷却过程中易出现单层G.P.区,而岩体的大小,冷却的快慢可能影响G.P.区的密度。对N-14样品不同放大倍数的高分辨象G.P.区线密度和面密度的统计值同样具代表性。文中设想了G.P.区出溶的假二元系相图。     

湖泊沉积物中重金属的环境地球化学

概要地回顾了近年来国内外湖泊沉积物中重金属环境污染方面的研究成果,介绍了湖相沉积物重金属研究的主要内容、方法和可能的发展方向。认为就重金属成因方面应加强区分其主要来源是岩石和矿物风化的碎屑产物、大气降尘、人类活动等的研究;重金属污染方面更应重视污染物质的生物有效性、迁移转化机理和重金属“二次污染”的研究;研究手段上,注重运用同位素示踪与定年技术来研究重金属的来源和污染历史,应用高分辨率沉积物钻心研究环境的变迁。最后提出加强多学科的综合研究,建立中国湖泊基准数据库,为探讨湖泊湿地的可持续发展提供依据。     

Geochemistry of an Island-Arc Plutonic Suite: the Uasilau-Yau Yau Intrusive Complex, New Britain, P.N.G

In the Uasilau-Yau Yau intrusive complex of central New Britain,Papua New Guinea, there is a compositional continuum in intrusiverock-types from gabbro to granodiorite and K-Ar mineral agesof the most mafic and most felsic components are not significantlydifferent (29?0.6 Ma versus 28.3?0.5 Ma, respectively). Tonaliteporphyry, the progenitor of porphyry copper mineralization inthe complex, represents a significantly younger intrusive eventat 24 Ma. Relatively calcic (An_95—50) plagioclase coresand salite to augite composition clinopyroxene are texturallyearly phases in the intrusive rocks. The main mafic mineral,calcic amphibole, generally has corroded clinopyroxene coresand may, like biotite, K-feldspar and quartz, generally be alate-stage, not a primary liquidus phase. Petrographic featuresindicate that the mafic minerals in the plutonic rocks crystallizedfrom melt, rather than being restite phases. The intrusive rocks cover an extensive silica range (45–75wt. per cent), do not exhibit simple straight-line variationon Harker diagrams for many elements (e.g. TiO₂, FeO, P₂O₅ andSr), and most are relatively depleted in incompatible traceelements (Rb, Zr, and REE). Major and trace element modellingsupports derivation of the complex by shallow level fractionalcrystallization dominated by removal of the phases calcic plagioclase,clinopyroxene, and magnetite from a parental magma closely resemblingrecent basaltic rocks in New Britain. The fact that the plutonicrocks are almost chemically indistinguishable from late Cainozoiccalc-alkaline volcanic rocks of New Britain supports fractionalcrystallization as a viable mechanism for generating these island-arcvolcanic rocks and indicates an analogous origin for the initialmagma. Granites, such as those of the Uasilau-Yau Yau intrusive complex,which are probably generated by partial melting of subductedoceanic crust or the overlying mantle, may be termed mantleor M-type granites. Documentation of the characteristics ofM-type versus normal I-type granites may enable the recognitionof M-type plutonic rocks in older, possibly more deeply erodedgeologic terrains. This would, by analogy to their volcanicequivalents, be very helpful in tectonic interpretations. Also,such plutonic rocks have known potential for Cu-Au mineralization.