Gemstones and geosciences in space and time

Dill, Harald G.; Weber, Berthold

doi:10.1016/j.earscirev.2013.07.006

Cited by 8 publications

(3 citation statements)

References 84 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is the most recent type of placer and is only found next to ancient smelters where fayalite was washed out from dumped Fe slags. This example was selected to raise awareness among exploration geologists of the wide range of artificial chemical compounds in modern stream sediments that have been derived from production sites and may make false claims by simulating gemmy material [49]. [41] with an amendment by the author with regard to gemstones.…”

Section: Chemical Parametersmentioning

confidence: 99%

“…The platform for a more detailed discussion of gemstones in placer deposits and their integration into the overall classification scheme of magmatic, structurebound, sedimentary, and metamorphic mineral deposits is the "Chessboard" classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium", which was supplemented by a series of digital maps with a description of each gemstone group. All known gemstone groups worldwide were treated by country, geology, and geomorphology on 99 digital maps [1,49]-see Appendix A. For the current placer-type deposits the distribution of gemstone deposits the reader is referred to the geomorphological maps as the most relevant tool to get an insight into the enrichment of gemstones worldwide.…”

Section: Gemstone Placers From Beryl To Zirconmentioning

confidence: 99%

“…To allow for a direct correlation of the "Chessboard classification scheme of mineral deposits" [1] and its special edition of digital maps of gemstone deposits [49]; with the current study of placer deposits which is designed as a more detailed treatment of those commodities also of significance for gems and gemstones, the pertinent tables from the "Chessboard classification scheme of mineral deposits" are listed below. The gemstone placer deposits under study in the current review can be linked to the primary magmatic, metamorphic and structure-bound deposits which are the potential source of the gems and gemstones in the placer deposits around the globe.…”

Section: Synopsis and Conclusionmentioning

confidence: 99%

See 2 more Smart Citations

Gems and Placers—A Genetic Relationship Par Excellence

Dill¹

2018

Minerals

View full text Add to dashboard Cite

Gemstones form in metamorphic, magmatic, and sedimentary rocks. In sedimentary units, these minerals were emplaced by organic and inorganic chemical processes and also found in clastic deposits as a result of weathering, erosion, transport, and deposition leading to what is called the formation of placer deposits. Of the approximately 150 gemstones, roughly 40 can be recovered from placer deposits for a profit after having passed through the “natural processing plant” encompassing the aforementioned stages in an aquatic and aeolian regime. It is mainly the group of heavy minerals that plays the major part among the placer-type gemstones (almandine, apatite, (chrome) diopside, (chrome) tourmaline, chrysoberyl, demantoid, diamond, enstatite, hessonite, hiddenite, kornerupine, kunzite, kyanite, peridote, pyrope, rhodolite, spessartine, (chrome) titanite, spinel, ruby, sapphire, padparaja, tanzanite, zoisite, topaz, tsavorite, and zircon). Silica and beryl, both light minerals by definition (minerals with a density less than 2.8–2.9 g/cm3, minerals with a density greater than this are called heavy minerals, also sometimes abbreviated to “heavies”. This technical term has no connotation as to the presence or absence of heavy metals), can also appear in some placers and won for a profit (agate, amethyst, citrine, emerald, quartz, rose quartz, smoky quartz, morganite, and aquamarine, beryl). This is also true for the fossilized tree resin, which has a density similar to the light minerals. Going downhill from the source area to the basin means in effect separating the wheat from the chaff, showcase from the jeweler quality, because only the flawless and strongest contenders among the gemstones survive it all. On the other way round, gem minerals can also be used as pathfinder minerals for primary or secondary gemstone deposits of their own together with a series of other non-gemmy material that is genetically linked to these gemstones in magmatic and metamorphic gem deposits. All placer types known to be relevant for the accumulation of non-gemmy material are also found as trap-site of gemstones (residual, eluvial, colluvial, alluvial, deltaic, aeolian, and marine shelf deposits). Running water and wind can separate minerals according to their physical-chemical features, whereas glaciers can only transport minerals and rocks but do not sort and separate placer-type minerals. Nevertheless till (unconsolidated mineral matter transported by the ice without re-deposition of fluvio-glacial processes) exploration is a technique successfully used to delineate ore bodies of, for example, diamonds. The general parameters that matter during accumulation of gemstones in placers are their intrinsic value controlled by the size and hardness and the extrinsic factors controlling the evolution of the landscape through time such as weathering, erosion, and vertical movements and fertility of the hinterland as to the minerals targeted upon. Morphoclimatic processes take particular effect in the humid tropical and mid humid mid-latitude zones (chemical weathering) and in the periglacial/glacial and the high-altitude/mountain zones, where mechanical weathering and the paleogradients are high. Some tectono-geographic elements such as unconformities, hiatuses, and sequence boundaries (often with incised valley fills and karstic landforms) are also known as planar architectural elements in sequence stratigraphy and applied to marine and correlative continental environments where they play a significant role in forward modeling of gemstone accumulation. The present study on gems and gemstone placers is a reference example of fine-tuning the “Chessboard classification scheme of mineral deposits” [1] and a sedimentary supplement to the digital maps that form the core of the overview “Gemstones and geosciences in space and time” [2].

show abstract

Section: Chemical Parametersmentioning

confidence: 99%

Section: Gemstone Placers From Beryl To Zirconmentioning

confidence: 99%

Section: Synopsis and Conclusionmentioning

confidence: 99%

See 1 more Smart Citation