Terrigenous rocks

Earth s crust is a source of particles produced as a consequence of weathering and volcanic activity. Weathering of continental rocks generates terrigenous particles that are carried into ocean via rivers, glaciers, and winds. As shown in Table 13.2, the most abundant mineral types are quartz, plagioclase, and clay minerals. The most abimdant... 

The cations become a component of river water and are eventually transported to the sea. About 45% of the dissolved solids entering the ocean are derived from the weathering of detrital silicates. Feldspars are the most important somce rock for terrigenous clays as illustrated by the following reaction... 

This deposit is located in the north-east of Russia and belongs to a gold-arsenic type of low-sulphide formation (Abramson et al, 1980). It lies within a carbonaceous terrigenous rock of Triassic age and is associated with a dome-shaped uplift in a node of intersecting faults of various directions. The ore bodies consist of zones of silicification and kaolinization with veinlet-disseminated sulphide mineralisation. Gold is present in the form of finely-dispersed dissemination in arsenopyrite and pyrite. As an example. Figure 1 illustrates the distribution of Au and Mn in connection with commercial ore... 

The occurrence of kaolinite is generally erratic but in the terrigenous sediments (Muffler and White, 1969) it can apparently react with dolomite to form the assemblage calcite + chlorite between 120-180°C. Expandable chlorite was noted in shear zones, and iron-rich chlorite is common in most of the rocks becoming more evident at greater depths. In the terrigenous rocks observed, the apparent alumina content of chlorite decreases with depth. Alkali zeolites have been observed at temperatures up to 100°C in the deeply buried rocks. 

Besshi deposits comprise thin sheets of massive, well-layered pyrrhotite - - chalcopyrite + sphalerite - - pyrite with minor galena and cobalt minerals interlayered with terrigenous clastic sedimentary rocks and calc-alkaline... 

Powell T. G. and Boreham C. J. (1991) Petroleum generation and source rock assessment in terrigenous sequences an update. APEA J. 31, 297-311. 

The sedimentary cover is stratified and consists mostly of calcareous-terrigenous rocks of Mesozoic and Cenozoic age up to 3-4 km thick. They form gentle... 

The Witwatersrand Basin The best known late Archaean sedimentary basin is the Witwatersrand Basin, for it hosts the world s richest gold province and is also an important source of uranium. For these reasons the geology of this basin is known in considerable detail. The Witwatersrand basin contains a 7 km-thick succession of terrigenous sediments and volcanic rocks, formed between 3.074 and 2.714 Ga ago. 

The average framework compositions of the four depositional sequences are reported in Table 1. The triangular plots of Fig. 4 show the composition of the total framework (Fig. 4A), the terrigenous framework (Fig. 4B) and the fine-grained rock fragments (Fig. 4C). 

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