Coupling mechanism of mineralization and hydrocarbon-forming in hydrothermal convection system: An example from Longtoushan Sn-polymetal deposit, Dachang

Longtoushan Sn-polymetal deposit is a large-scale deposit of high-tenor. The ore-bodies occur in reef limestone of middle Devonian. There is much anthraxolite in reef limestone and ore-bodies. The anthraxolite is the postmature result of oil-gas' thermal metamorphism. The close relationship of anthraxolite and Sn-polymetal deposit reveals the space-time relation between oil-gas evolution and Sn-polymetal mineralization. Sulfur isotope of Longtoushan deposit is close to oil's sulfur in Devonian, which indicates obvious relationship between the sulfur's source of deposit and oil-gas' activity. The forming of Longtoushan deposit relates to exhalative-sedimentary mineralization in Devonian. Because of the favorable hydrocarbon-forming condition of Longtoushan reef and surrounding basin facies' black shale and peat, coupling of ore-formation and hydrocarbon-forming occurs in seabed's hydrothermal convection. The distributing of ore-forming elements indicates the presence of hydrothermal convection system. The thermal fluid containing organic matters conduces to Sn-polymetal elements' activation and transfer, and provides catalyzing condition to the transforming from SO42- to S2-. The erosion action of brine containing organic acid to reef limestone induces the growing of crannies and karst's caverns, which provides advantageous space to Sn-polymetal mineralization. The heat source of mineralization provides thermocatalysis condition to hydrocarbon-forming. When the circulatory fluid containing oil-gas enters the high-temperature region(＞150 ℃ ), the oil-gas is decomposed and anthraxolite comes into being.

Characteristics and Sources of Organic Matter from the Early Cambrian Niutitang Formtion and Its Preservation Environment in Guizhou

The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock.However,hydrocarbon-forming organisms of these organic-rich shales was poorly understood.In this paper,the results of palynofacies analysis and hydrocarbon-forming organism characteristics of the Niutitang Formation from the Yangtze Block are reported for the first time,and the sedimentary environment is discussed in combination with geochemical data.Palynofacies analysis show that the organic matter(OM)of the Niutitang Formation is mainly composed of amorphous organic matter(AOM),with a small amount of structural organic matter(STOM)and palynomorphs(PL).The results of CONISS(stratigraphically constrained incremental sum of squares)cluster analysis show that the PL can be divided into three zones in the ascending order:Leiosphaeridia-Micrhystridiumfungal zone,algal bloom zone and fungal development zone,corresponding to three stages:transgression,high-stand and regression,respectively.The principal component analysis(PCA)shows that the main hydrocarbon-forming organisms include planktonic green microalgae or dinoflagellates that are related to Leiosphaeridia and Microcystidium.Palynofacies analysis and geochemical data show that the Niutitang Formation was deposited under anoxic or dysoxic condition which was favorable to the enrichment of organic matter.