Geochemical and geological properties of tin related to ore deposits: A Review

Tin have atomic number 50 and atomic mass 118,71, commonly found as cassiterite in nature. It is one of important elements in low carbon technologies. Nowadays, tin utilized in broad application range from tin can to electronics. Despite many uses, tin is only produced from limited areas. Because of broad application, understanding of tin in nature is important. Tin usually can be found together with wolfram, although it often occurs at different locations. Tin may occur in various ore deposit types such as greisen, vein, skarn, and placer. This article will describe the geochemical and geological properties of tin in nature, especially that related to ore deposits.


Introduction
Tin is one of the important elements in green technology.Besides used in green technology, tin also used in tinplate, alloy, solder, and bar tin [1].Researcher found and studied tin deposits around Atlantic Ocean namely Andean Belt, East Brazilian Belt, Rondônia-Guyana Belt, Rocky Mountain Belt, Appalachian Belt, Central African Belt, South West Africa-Nigeria Belt, Iberian Belt, Armorican Belt, and Erzgebirge Province [2].Besides that, tin also can be found in Southeast Asia Tin Belt in which most of tin (more than 50%) originated from [3]. Figure 1 shows the global tin deposits location with historical production.The global tin consumption increased from around 250 Gg in 1999 to 381 Gg in 2017 with the biggest producers being China, Indonesia, and Myanmar.Currently, tin produced by China and Myanmar are used by China, that has become the largest tin consumer in the world replacing the US and European Union.Tin consumption increase in China is the biggest contributor to global tin consumption raise [6].
Concentration of tin in bulk crust is around 1.7 ppm with concentration in upper crust around 2.1 ppm and in lower crust around 1.1 ppm [4].Meanwhile the lowest percentage of mineable tin deposits are around 0.1 percent with most of the deposits ranging from 0.25 0.75 percent [7].Additionally, each deposit type shows a different tonnage and Sn grade with highest grade contained in lode while greisen shows low grade-high tonnage characteristics (Figure 2).

Geochemical properties of tin
Tin atomic number is 50 with electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 2 or [Kr] 5s 2 4d 10 5p 2 [8].Tin in nature can be found as Sn 2+ (ionic radii 1.12 angstrom) or Sn 4+ (ionic radii 0.71 angstrom) [9].Sn 4+ ionic radii are similar to Fe 3+ (0.64 angstrom), Ti 4+ (0.68 angstrom), Nb 5+ (0.68 angstrom), Ta 5+ (0.69 angstrom), and Sc 3+ (0.81 angstrom) [10].Thus, tin ion can be substituted by those ions, and vice versa.The substitution mechanism can be divided into trivalent, tetravalent, pentavalent, and hexavalent [11].Table 1 shows the substitution mechanism of tin in cassiterite that divided into several classes.Sn and 121 Sn not stable with half-life 113 days and 27 hours, respectively [12].Besides as parent element, Sn also product of other element radioactive decay (daughter element).It is commonly identified as a daughter element of indium and antimony.But most half-life of tin parent elements short, ranging from minutes to several seconds (Table 3).Thus, we can assume that all of parent elements already decayed to tin.Variation of tin isotope in cassiterite observed in several observation, and was caused by fluctuations in mineralizing fluid (Figure 3).Core-rim cassiterite mineral compositions study by laser ablation shows that fluid evolution can occur in fluid episode that result in lighter tin isotope as well as lower Ta concentration [17].Besides that, the results also shows that tin mineral can be formed by more than one fluid episodes.Most important tin mineral is cassiterite that contain 78.8 percent tin and chemical formula SnO2.
Because cassiterite is very resistant to weathering and can be classified as heavy mineral (7.15 g/cm 3 ), many cassiterite accumulates in heavy mineral sands, and profitable to be mined [4].Besides cassiterite, other important tin minerals are stannite, herzenbergite, nordenskioldine, and malayaite in which listed in Table 4. Study shows that in system with low acid volatile like skarn, malayaite and Sn bearing calc-silicate mineral stable, while in system that rich in B2O3, CO2 and F2O like greisen, cassiterite stable except in system with low SiO2 and rich B2O3, nordenskioldine can develop [19].Cassiterite is the most important tin mineral, becoming a subject in various studies to understand the characteristics of it.Geochemistry of cassiterite as well as trace elements in cassiterite research shows that cassiterite mineral shows banded geochemical substitution of Sn 4+ with Zr, Ti, Fe, Mn, Nb, Ta, and W, with W, Fe, Nb, and Ta shows sector zonation [11].
Besides in tin ore mineral as mentioned in Table 4, tin may also present in other minerals as impurities in ore deposits.Tin concentrations in various minerals in Furong tin deposits study discovered that tin concentrations in minerals related to skarn process relatively high up to around 44000 ppm (Table 5) [20].It is also noted that tin impurities concentrations in those minerals related to substitution of Al vi in magnetite and silicate as well as replace Fe 3+ in epidote and low Al vi silicates.

Geological properties of tin
Primary tin deposits usually occur in syn-subduction tectonic setting.It usually related to highly fractionated low oxidation granitic intrusions [21] (Figure 4) that melt enriched tin sedimentary sources (S-type) [22].Sedimentary tin deposits developed by weathering rocks that contain tin minerals, e.g., cassiterite.Because of its resistance to weathering and characteristics, cassiterite will be enriched in heavy mineral sands.Tin deposits can be classified as several different types, depending on the classification scheme.Dill [10] divided tin deposits into two large groups namely magmatic and sedimentary tin deposits.Magmatic tin deposits consist of pegmatite, granitic skarn, greisen-vein and breccia pipe, porphyry, and volcanic massive sulfide (VMS).Additionally, sedimentary tin deposits consist of SEDEX, laterite (residual placer) and placer deposits related to alluvial-fluvial and marine (Table 6).

Table 6 Tin deposits classification [10]
Classification scheme for tin deposits (1) Magmatic tin deposits (1) Sn-Ta-Nb pegmatites (2) Granitic skarn deposits (1) Proximal Sn-(W) skarn deposits (Erzebirge-Cornwall-type) (2) Distal skarn/replacement deposits (Manto-type) (3) Post-granitic endo-and exogranitic greisen-vein in S-and A-type granites and breccia pipe deposits (4) Porphyry-type and subvolcanic deposits (1) Sn-(Ag-Pb-Zn-Cu) vein-type deposits (5) Stratiform Sn-W deposits (6) Volcanic massive sulfide Pb-Zn-Cu deposits (VMS) (1) Iberian-type (2) Sedimentary tin-tungsten deposits (1) SEDEX/SMS Pb-Zn-Ag-FeS-(Sn) deposits (2) Sn laterite (residual placer) deposits (3) Sn placer deposits (1) Alluvial-fluvial (2) Marine Geologically, tin enrichment in granitic rocks has taken place because melt produced from Sn rich source, fractional crystallization continued by hydrothermal process, or restite enrichment from melt extraction [23].Tin in nature is contained in common rock-forming minerals such as muscovite, biotite, titanite, and rutile so tin will not be enriched if those minerals are not melted [23].This phenomenon is well recorded in Nanling Region, China where granites products from lower temperature melting process did not host Sn, but higher temperature product from higher temperature biotite-dehydration process contains Sn [24].Other observation from metamorphism process shows that tin concentration in biotite and muscovite decreases as metamorphism occur, suggesting that the tin released and enriched in melt (Figure 5) [25].Figure 6 shows tin concentration in biotite from granite that can reach up to 1000 ppm.Petrological experiment shows that Cl and F are important as solubility control of SnO2 in peraluminous melt with oxygen fugacity near Ni-NiO with strong effect from temperature, oxygen fugacity as well as Al concentration [26].Many researchers show correlation between tin deposits and specific regions globally.Study shows that tin deposits can be developed because of accumulation of tin-enriched sedimentary rocks subjected to heat that led to melting and release of tin to fluid [22].The heat itself is not restricted to specific tectonic settings.Link between enriched protolith and tin deposits also observed by other researchers from examination of tin mineralization around Atlantic.Tin mineralization around Atlantic is believed to develop because they linked with tin rich areas [2].Besides that, observation in tin fertile granite, shows low concentrations of tin that indicates scavenging of tin from granitic rocks by later hydrothermal fluids [28].
Tin is usually transported as chlorine complex in hydrothermal fluids, either as SnCl2 [29] or SnCl4 [30].HCl molality is the important parameter for tin transport and precipitation, thus tin can be precipitated because of HCl molality change caused by fluid-wall reaction, dilution, as well as boiling [31].Fluid-wall reaction caused HCl neutralization and tin precipitation.There are different mechanisms in HCl neutralization in carbonate (dissolution) and schist (conversion feldspar and biotite to muscovite) [32].Dilution is another method to precipitate tin.This method decreases HCl concentration by mixing mineralizing fluid with low HCl concentration fluid (e.g.meteoric fluid), thus encouraging tin precipitation [31].Additionally, tin precipitation may be encouraged by boiling process.The process may be induced by fault activity that led to vapor loss and precipitation of tin [30].

Conclusions
Tin can be found as ten different isotopes in the nature, with three largest tin isotope abundance in nature are 120 Sn (32.58%), 118 Sn (24.22%), and 116 Sn (14.54%).Tin may be replaced by other elements, such as Fe, Mn, Si, Ti, W, Nb, Ta and Zr by trivalent, tetravalent, pentavalent, and hexavalent substitutions.Variations in tin isotopes may reflect mineralization history of ore minerals.Many tin deposits developed in tin-rich protolith suggest the importance of protolith enrichment in tin deposit genesis.Cassiterite (SnO2) is the most important tin mineral with other tin minerals such as stannite, herzenbergite, nordenskioldine, and malayaite may be found.Because cassiterite is resistant to weathering and high-density characteristics, many tin deposits are formed in heavy mineral sands.Tin transport and precipitation are mainly controlled by concentration of HCl, and mechanisms that can affect the HCl in fluid such as fluid-rock interactions, fluid mixing and vapor loss due to degassing.

Figure 1
Figure 1 Distribution of tin deposits around the world with black rectangles showing areas with historical tin production [4].Coastline adapted from North American Cartographic Information Society [5]

Figure 2
Figure 2 Global ore grade-contained Sn diagram of tin deposits [7]

Figure 4
Figure 4 Oxidation-fractionation graph of various metal deposits [21].Tin (red box) marked with high fractionated low oxidation.

Figure 5
Figure 5 Tin concentrations from biotite and muscovite minerals based on LA-ICP-MS analysis related to metamorphism [25].The yellow boxes and green boxes, respectively, are areas where muscovite melting (650-760˚C) and biotite melting (740-940˚C) occur.Dotted line represents muscovite mineral data trend, while solid line represents biotite mineral data trend.

Table 2
).Most of tin isotope are stable, only 113