Arsenic, antimony, bismuth, nitrogen, phosphorus

1. Arsenic, antimony, bismuth, nitrogen, phosphorus

3. Arsenic (As) Universe: 0.008 ppm (by weight)  Carbonaceous meteorite: 1.8 ppm Earth's Crust: 1.5 ppm  Seawater:  1.45 x 10-3 ppm

4. Arsenic in magmatic processes The average content of arsenic in igneous rocks is approximately 1.5 ppm, but is higher in sedimentary rocks (5-10 ppm). It concentrated mainly to post-magmatic processes. Naturally occurring arsenic minerals include native arsenic, oxides, arsenates, sulfides and arsenides. Native arsenic is relatively rare, while the most common arsenic-bearingmineral is arsenopyrite, FeAsS, which is a ubiquitouscomponent of many sulfidic ore deposits. Other common arsenicsulfides include orpiment As2S3 (yellow), and realgar AsS(red/orange), which occur in hydrothermal veins and are particularlyconspicuous in the highly colored sinters.

5. Arsenic in magmatic processes Arsenides such as löllingite, FeAs2 and rammelsbergite, NiAs2 , occur in deeper, higher temperature vein deposits. A variety of mixed metal arsenides and arseno-sulfides (so-called sulphosalts) also occur in ore deposits, e.g. proustite Ag3AsS3, tennantite Cu12As4S13. It often substitute S in pyrite, and Sb in some sulphosalts.

6. Arsenic in weathering and sedimentary processes Arsenic oxides and arsenate minerals form as supergene minerals during the oxidation of arsenic-bearing oredeposits. Arsenic oxide (As2O3), the main form of arsenicused as a deliberate poison and known as 'white lace', formsnaturally in this way. We knowmany arsenates (AsO4salts) in the oxidation zone of ore deposits (e.g. scorodite FeAsO4 • 8H2O, mimetite Pb5(AsO4)3Cl, olivenite Cu2(AsO4)(OH), annabergite Ni3(AsO4)2 • 8H2O, erythryne Co3(AsO4)2 • 8H2O. Naturally occurring arsenites (AsO3 salts) are rare. However, as arsenic is readily adsorbed onto, orco-precipitated with, iron oxides and sulfides, it will often occuras a secondary component of these minerals rather than as a discreete mineral phase.

7. Arsenic in weathering and sedimentary processes Most arsenic compounds are sparingly soluble in water. Naturalfreshwaters generally contain arsenicconcentrations of< 1 ppb, but natural rivers and lakes with arsenic concentrationsof > 10 ppb are not uncommon and hot spring fluidsmay contain up to 8-10 ppm. In mildly reducing waters such as geothermal hot springs and groundwaters,arsenious acid H3As03 will usually be the most common dissolved arsenic compounds present. In sulfide-rich environments arsenic may be complexed withsulfide ligands (e.g. H2As3S6). The oxidation of As3+ to As5+ is slow in near-neutral pH solutions, unless catalyzed by bacteria.

8. Arsenic in weathering and sedimentary processes Both As3+ and As5+ are readily adsorbed onto clays and hydrous iron oxides in natural waters. Arsenic adsorption ontoiron oxides occurs more readily at acid pH, and consequentlyarsenic can be preferentially removed from acid effluents (suchas acidified mine drainage) by natural precipitates of iron oxide. Although natural arsenic concentrations are mainly limited by such adsorption processes, arseniccan also be removed by mineral precipitation if highconcentrations are present. Scorodite and orpiment may bedirectly precipitated from weathering and geothermal fluids respectively.

10. Antimony (Sb) Universe: 0.0004 ppm (by weight) Sun: 0.001 ppm (by weight) Carbonaceous meteorite: 0.12 ppm Earth's Crust: 0.2 ppm Seawater: 2 x 10-4 ppm

11. Antimony in magmatic processes Antimony is enriched in intermediate andfelsic volcanic rocks and in intermediate intrusive types. Asystematic increase in concentration in volcanic rocks frommafic ( < 1.0 ppm) to felsic (7 .8 ppm) varieties is apparent. Antimony is most concentrated in the lithosphere in low temperature hydrothermal ore deposits. A large number of processes may cause the precipitation of antimony from hydrothermalsolutions: decrease in temperature, neutralization ofbasic or acidic solutions, oxidation etc. Stibnite (Sb2S3) and some Sb-bearing sulphosalts have been identified as a sublimate in a number of modern volcanoes.

12. Antimony in magmatic processes The most common natural form of the element is the sulfide mineral, stibnite orthorhombicSb2S3. Antimony is occasionally found as anative metal or as an intermetallic compound with arsenic.Over 113 different sulfide, antimonide, arsenide and tellurideminerals have been identified. Sulfosalts represent the mostvarious antimony-bearing minerals, usually in some combinationwith silver, copper, arsenic, mercury, lead and, rarely,thallium, iron, cobalt, nickel, etc. Over 35 oxide, hydroxide and oxyhalide mineral species are known.

13. Antimony in weathering and sedimentary processes In general, the concentration of antimony in sedimentary rocks is less than 1.0 ppm. Fine-grained sedimentary rocks, especially pyritic types, contain the highest concentrations.Coal is strongly enriched in antimony compared tomost rock types although there is no apparent mechanism to explain this enrichment. There are common oxides of Sb in the oxidation zone of Sb-bearing ore deposits (e.g. stibiconite, valentinite, cervantite), and rare antimonates (with the SbO4 anion), too.

14. Bismuth (Bi) Universe: 0.0007 ppm (by weight) Sun: 0.01 ppm (by weight) Carbonaceous meteorite: 0.07 ppm Earth's Crust: 0.048 ppm Seawater:    Atlantic surface: 5.1 x 10-8 ppm

15. Bismuth in magmatic processes Bismuth displays little variation between different rock types. It is found in similar concentrations in mafic and intermediaterocks, intrusive or extrusive, around 0.04 ppm. It is markedlyenriched in felsic rocks: 0.9 ppm in rhyolite and 0.27 in granites,although not all granites display consistent enrichment. It concentrates in post-magmatic processes from the pegmatite (complex oxides with Nb-Ta), to the high and medium temperature hydrothermal stadiums. The majority are sulfides and sulfosalts, which occur mostoften in association with lead and silver, although copper,nickel, iron, and mercury varieties are also reported.

16. Bismuth in magmatic processes Otherprimary bismuth minerals include tellurides, selenides and bismuthides. The most common Bi mineral is bismuthinite(Bi2S3). Bismuthinite closely resembles stibnite (Sb2S3 ), withwhich it forms a complete solid solution. Characteristic Bi minerals are the tellurides, from which some mineral were described in the Carpathain Mts. e.g. pilsenite, tetradymite, vihorlatite.

17. Bismuth in weathering and sedimentary processes No marked concentration preference within various types of sedimentary rocks is apparent, although concentrations tendto be higher in recent pelagic sediments (0.56 ppm). Shalesgenerally display the highest concentrations of bismuth,average 0.26 ppm, and sandstones and limestones average0.03 ppm. Coal is greatly enriched (average 5.0 ppm), althougha mechanism for the enrichment is unknown. Secondary species of bismuth occur as oxides (bismite, spherobismoite), vanadates, molybdates, arsenates, sulphates, and tungstates, but these phases rather rare.

18. Nitrogen (N) Universe: 1000 ppm (by weight) Sun: 1000 ppm (by weight) Carbonaceous meteorite: 1400 ppm Earth's Crust: 25 ppm Seawater:    Atlantic surface: 8 x 10-5 ppm Atlantic deep: 2.7 x 10-1 ppm

19. Nitrogen in magmatic processes Most crustal rocks (except for organic-rich sediments) contain < 0.1% N, and mantle-derivedrocks and magmas mostly contain < 20 ppm N. Theabundance of N in the Earth's core is not known, but itsabundance in iron meteorites (up to 100 ppm) suggests thatthe core could be a significant minor reservoir of nitrogen. The minerals which contain essential ammonium are rare, but many rocks contain the ammonium ion as a minor constituentof feldspars, micas or clay minerals, in which it substitutesisomorphously for potassium (ionic radii: K+ 1.63 A, NH4+ 1.69 A). Some N-bearing minerals have been recorded only from volcanic sublimates (e.g. sal ammoniac cubic NH4Cl).

20. Nitrogen in magmatic processes Ammonium is very readily mobilized byhydrothermal activity, and many hydrothermally altered rocks show strong NH4 enrichment. The ammonium content of hot spring waters varies from zero up to > 1000 ppm. Sulfates, especially ammonioalunite and ammoniojarosite, are also characteristic of recent hot springmineral deposits. The ammonium silicates are also present inolder mineral deposits, being more insoluble than most of the ammonium-bearing non-silicates. Silicate minerals which contain essential ammonium are buddingtonite (ammonium feldspar), tobelite (ammonium mica), and ammonium illite.

21. Nitrogen in weathering and sedimentary processes Ammonium that is present in sedimentary rocks is nearly all derived from the decay of nitrogen-bearing organic material.Seawater does contain a small amount of free ammonium ionwhich can be incorporated in sedimentary minerals at the timeof deposition. Many organic compounds contain nitrogen,but the most important contributions come from twosources: (a) the proteins of animal and plant tissues and theirbreakdown products, and (b) urea and related products ofanimal metabolism. Subsequent to burial, the organic compoundsin sediments are subject to hydrolysis and oxidation,and their nitrogen is partly converted to N2 and partly to ammonia.

22. Nitrogen in weathering and sedimentary processes The nitrogen that is present in sedimentary rocks is thereforedivided into three main categories: (a) organic nitrogen,(b) ammonium ion held in an exchangeable form by absorptiononto the surface of clay minerals, or in clays and other mineralshaving a cation exchange capacity, or in interstitial fluids, and(c) ammonium ion fixed in the crystal structures of stablesilicate minerals such as feldspars or micas.Nitrogen-bearing minerals contain either the nitrate ion(NO3) or the ammonium ion (NH4). Niter (KNO3) and soda-niter (NaNO3) occur abundantly in Chilean nitrate deposits, sporadically in the soils of other arid regions, and occasionally in decaying animal matter in limestone caves.

23. Nitrogen in weathering and sedimentary processes About 30 ammonium minerals are known, including several of each of the following groups: halides, sulfates, borates, phosphates and silicates. Most of the ammonium minerals are water-soluble and, like the nitrates, they are veryrestricted in their distribution. Most commonly they occur asweathering products of organic-rich sediments such as lignite, coal or guano. Various ammonium sulphates form by slow burning of organic matter in waste dumps of coal mines.

24. Phosphorus (P) Universe: 7 ppm (by weight) Sun: 7 ppm (by weight) Carbonaceous meteorite: 1100 ppm Earth's Crust: 1000 ppm Seawater:    Atlantic surface: 1.5 x 10-3 ppm Atlantic deep: 4.2 x 10-2 ppm

25. Phosphorus in magmatic processes Elemental phosphorus is never found free in nature because it readilyoxidizes to phosphate and spontaneously combusts in air.The most common phosphorus-bearing mineral is the phosphate apatite (group) Ca5(PO4)3(OH,F,Cl).Largeamounts are found in veins associated with alkalic rocks. Apatite can concentrates large amounts in early differenciates. The phosphates are various compounds, we known about 400 phosphate minerals. The most important are: apatites, monazite, and xenotime, all essentially rock-forming components. There are various subsitutions in apatite minerals, both the cation and anion pozitions.

26. Phosphorus in magmatic processes Characteristicphosphatemineralsinpegmatite: Ambligonite - (Li,Na)Al(PO4)(F,OH), Berillonite - NaBePO4, Triphylite - LiFePO4, Triplite - (Mn,Fe,Mg,Ca)2(PO4)(F,OH). Therearemanyphosphateswithvariouscompoundsintheoxidationzone of oredeposits: pyromorphite - Pb5(PO4)3, turquoise - CuAl6(PO4)4(OH)8  8H2O etc.

27. Phosphorus in weathering and sedimentary processes In soils, Pconcentrations range from 0.022 to 0.83%, but only a small fraction of this isbioavailable for plant and microbial uptake. The concentrationof Pin seawater is highly variable, averaging about 70 11g/l. PO4 , while in river waters its concentration is about 20 11g/lPO4 . Phosphorus is thought to be the limiting nutrient in numerous freshwater systems, because its input in large quantitiesresults in excessive algal and rooted aquatic plant growth. Uranium, Th and rare earths are often associated with phosphateminerals and high U and Ra concentrations in somegroundwaters reflect the presence of these secondary minerals.

28. Phosphorus in weathering and sedimentary processes Chemical stabile phosphates can accumulate in clastic sediments, e.g. monazite, xenotime, and partly apatite. However, the larger part of phosphorus concentrate in sedimentary rocks, such marine phosphatites (their rock-forming minerals are apatites). Important phosphate accumulations are in guanos with characteristic minerals, as taranakite, brushite, hydroxilapatite. In these rocks, the phosphate come from organic matters. One of most important phosphate mineral in reductive sedimentary environment is vivianite, monoclinic Fe3(PO)42 . 8H2O.