TIN 



643 



Table 134. — The more common tin minerals — Continued 



Name 



Compositit 



Geographic 



Herzenbergite 



Hielmite 



Hochschildite 

 Hulsite 



Malayaite 



Mawsonite 

 Native tin 



Nigerite 



Nordenskioldine 



Ottemannite 

 Paigeite 



Renierite __ 

 Sorensenite , 



Stannite 



Stokesite 



Sukulaite __ 



Teallite 



Thoreaulith 

 Varlamoffite 



_SnS Bolivia. 



_Y,Fe,Mn,Ca,Sn-niobate- Svi^eden. 



.PbSnOa'wH.O Bolivia. 



_12(Fe,Mg)0'2Fe203' Alaska. 



ISnOj- 3B.03'2H20. 

 -CaSnSiOs Malaya, 



Cornwall. 



-CU11.5Fe12.5Sn10.4S33 Tasmania. 



.Sn New South 



Wales. 

 -Complex tin silicate South West 



Africa. 

 -Ca,Sn (603)2 Norway, 



South West 



Africa. 



.Sn2S3 Bolivia. 



-SOFeO'SFe^Oa'lSnOz' Alaska. 



6B.03'5H=0. 

 -Cu3(Ge,Fe,Sn,Zn)Si ___ (?) 

 .NaiSnBe3Si60i6(0H)i —Greenland. 



-CU"FeSnSi Worldwide. 



-Ca,Sn(Si309)'2H:0 Cornwall. 



-TaoSn-Oi Norway. 



.PbSnS. Bolivia. 



-SnTasOT Congo. 



-H3Sn03 Do. 



compounds with tellurium and selenium, but only at 

 high temperatures and pressures, and no such min- 

 erals are known to occur in nature. Only in Bolivia 

 are many of the sulfide minerals present in sufficient 

 amounts to be recovered, and their recovery requires 

 a complex hydrometallurgical treatment. Stannite is 

 found in many tin-sulfide deposits, and small 

 amounts are recovered. Of all the coproducts or by- 

 products produced, tungsten is probably the most 

 important. 



TYPES OF DEPOSITS 



Tin is produced from six different types of lode 

 deposits, and from placer deposits. 



LODE DEPOSITS 



Lode tin deposits can be classified into six distinct 

 types, following the classification of Ahlfeld 

 (1958) : (1) pegmatite deposits, (2) pneumatolytic- 

 hydrothermal deposits, (3) subvolcanic or tin-silver 

 deposits, (4) disseminated deposits, (5) contact- 

 metamorphic deposits, and (6) fumarole deposits. 



PEGMATITE DEPOSITS 



Tin-bearing pegmatites are generally associated 

 with granitic rocks and contain cassiterite (SnOa), 

 as well as other uncommon, valuable minerals such 

 as columbite-tantalite, beryl, or spodumene. Most 

 productive pegmatites are in areas of deep tropical 

 weathering, which permits the economic exploita- 

 tion of pegmatites that contain less than 0.4 percent 

 tin. Some pegmatites are very large, contain cassi- 



terite throughout, and constitute major reserves of 

 tin; one example is the Manono pegmatite in the 

 Democratic Republic of the Congo, which is 10 

 kilometers long and 100-400 meters wide. 



PNEUMATOLYTIC-HYDROTHERMAL DEPOSITS 



Most of the major lode tin deposits of the world 

 (those of Bolivia excepted) are of the pneumato- 

 lytic- hydrothermal type. (This distinction of the Bo- 

 livian type of deposit from what may be called the 

 Cornwall type may not be valid. The authors here 

 are following most other workers, who consider them 

 in separate categories.) Lodes are near or in biotite 

 or two-mica granite and form replacement deposits 

 or fissure fillings in diverse types of country rock. 

 Owing to a regional zonation commonly displayed, 

 deposits vary widely in mineralogy. In or near gran- 

 ite, lodes typically contain cassiterite in greisen 

 (quartz-mica rock) or quartz-topaz-tourmaline rock 

 that also contains wolframite and many base-metal 

 sulfides. Farther from the granite, some lodes con- 

 tain stannite (Cu2FeSnS4), base-metal sulfides, and 

 silver; in some places, the deposit may be valued 

 principally for the silver content. Some individual 

 deposits are very large, such as the Dalcoath lode 

 in Cornwall, England, which produced 80,000 tons of 

 tin (Dines, 1956). 



SUBVOLCANIC OR TIN-SILVER DEPOSITS 



The subvolcanic or tin-silver type of deposit is 

 exemplified by the mineralogically complex and very 

 rich deposits of Bolivia, where bonanza tin lodes 

 also contain large amounts of silver. Deposition in 

 a near-surface environment led to strong telescoping 

 of the deposits and to mineralogical complexity, 

 which creates a problem in the recovery of tin. Rare 

 tin-bearing minerals, such as teallite, herzenbergite, 

 cylindrite, and eanfieldite, are common in these de- 

 posits. Individual mines in such deposits have pro- 

 duced enormous amounts of tin ; one mine at Llalla- 

 gua, Bolivia, produced over 500,000 tons (Ahlfeld, 

 1936). 



DISSEMINATED DEPOSITS 



In these deposits, cassiterite in small amounts is 

 disseminated widely in altered granite, especially in 

 border zones or parts changed by addition of tour- 

 maline, topaz, or fluorite. Although only a few dis- 

 seminated deposits are worked commercially at pres- 

 ent, erosion of such lodes (particularly border zones 

 of granites) has resulted in large and rich placer 

 deposits (Southeast Asia and elsewhere). 



CONTACT-METAMORPHIC DEPOSITS 



Contact-metamorphic deposits are fairly uncom- 



