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Petrography
About: Petrography is a research topic. Over the lifetime, 7449 publications have been published within this topic receiving 102018 citations.
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TL;DR: The most highly valued placer nephrite deposits in the world occur in the Yurungkash and Karakash Rivers (also known as the White and Black Jade Rivers) in Hetian, Xinjiang, Northwest China as discussed by the authors.
32 citations
TL;DR: In this article, a method to measure the distribution and concentration of wall rock minerals in open pit mines is presented, and applies the method to the Martha epithermal Au-Ag mine, Waihi, New Zealand.
32 citations
TL;DR: Petrographic and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source.
32 citations
TL;DR: The region of occurrence of zeolites in sedimentary rocks was first recognized by Coombs (1954) who made detailed petrographic studies of Triassic tuffaceous greywackes and tuffs of andesitic to rhyolitic in composition in the Taringatura area of New Zealand as discussed by the authors.
Abstract: Many zeolite assemblages originated during burial and subsequent low-grade metamorphism of rocks, particularly those of volcaniclastic origin. Eskola (1939) first suggested this type of zeolitization and applied the term “zeolite facies” to assemblages formed under such low-temperature and low-pressure conditions. Although several definitions of the “zeolite facies” have been proposed over the years (e.g. Fyfe et al. 1958), the phrase as used here includes both low-grade metamorphic assemblages and zeolite assemblages formed successively during burial.
The regional occurrence of zeolites in sedimentary rocks was first recognized by Coombs (1954), who made detailed petrographic studies of Triassic tuffaceous greywackes and tuffs of andesitic to rhyolitic in composition in the Taringatura area of New Zealand. Coombs recognized a zonal arrangement of heulandite and analcime near the top of the sequence and heulandite and laumontite near the bottom. He also recognized a similar progressive zeolitization with depth in clastic sediments in other orogenic belts. The zeolite assemblages described by Coombs represent a rather advanced stage of alteration, as opposed to an earlier stage of zeolitization that was subsequently described in Neogene silicic volcaniclastic rocks from Japan. In the latter rocks, zones (from top to bottom) of fresh glass, clinoptilolite + mordenite, analcime + heulandite, laumontite, and albite were recognized (Utada 1965, 1970). Progressive zeolitization has also been reported as a result of the thermal effects of intrusive masses (see Seki et al. 1969) and around volcanic calderas (Utada and Ito 1989). Recently, Boles (1991) described the low-temperature formation of laumontite and stilbite in fractures and faults related to post-Jurassic folding and uplift of the Southland Syncline, New Zealand.
The physico-chemical conditions of zeolite crystallization in burial diagenesis and low-grade metamorphic environments can vary widely. Both borehole data (see Iijima 1995) and experimental results (Liou 1970; 1971a,b,c …
32 citations