UNITED STATES MINERAL RESOURCES 



TIN 



By C. L. Sainsbury and Bruce L. Reed 



CONTENTS 



Page 



Abstract of conclusions 637 



Introduction 637 



Uses 638 



Supply 638 



Exploitation 639 



Relation to byproducts 639 



Environmental problems 640 



Geologic environment 640 



Geochemistry 640 



Geochemical cycle 641 



Tin minerals 642 



Types of deposits 643 



Lode deposits 643 



Pegmatite deposits 643 



Pneumatolytic-hydrothermal deposits 643 



Subvolcanic or tin-silver deposits 643 



Disseminated deposits 643 



Contact-metamorphic deposits 643 



Fumarole deposits 644 



Placer deposits 644 



Residual placers 644 



Eluvial (slope) placers 644 



Alluvial (stream) placers 644 



Marine placers 644 



Fossil placers 645 



Resources 645 



Identified resources 645 



Hypothetical resources 645 



Speculative resources 646 



Prospecting techniques 648 



Problems for research 650 



References cited 651 



FIGURE 



71. Diagram showing geochemical cycle of tin 



TABLES 



Ionic radii and electronegativity of ions similar 

 to Sn-* and Sn" 



Page 

 642 



Page 

 640 



133. 



134. 

 135. 



Page 



Range and average contents of tin in various 



materials 641 



The more common tin minerals 642 



Tin reserves and resources of the world 646 



ABSTRACT OF CONCLUSIONS 



The United States consumes almost 30 percent of the free 

 world's annual production of primary tin. Nearly half this 

 amount is used in the manufacture of tinplate, principally 

 for tin cans; the other main uses are in solders, bearing 

 alloys, bronze, chemicals, and coatings other than tinplate. 

 Many of these uses could be met by substitutes such as tin- 

 free steel, aluminum, or plastics. 



Current U.S. tin production, as a byproduct of molybdenum 

 mining in Colorado, is negligible. The strategic stockpile is 

 sufficient to guarantee against a sudden shortage of primary 

 tin for essential uses, but at the current rate of consump- 

 tion even this supply would be depleted in a little more 

 than 4 years. Domestic reserves of tin, mainly in Alaska, 

 would provide only about three-fourths of a year's supply, 

 conditional resources about the same, and hypothetical and 

 speculative resources about 2 years' supply; thus, it seems 

 clear that the United States must continue to depend on 

 tin imports for most of its needs. The largest foreign condi- 

 tional and undiscovered resources are in southeastern Asia, 

 Brazil, China, Bolivia, and Zaire. The worldwide geologic 

 association of tin with acid granitic rocks and rhyolites is 

 so well marked that speculation as to the likelihood of find- 

 ing major tin resources in new geologic environments is 

 without redeeming value. 



INTRODUCTION 



Tin metal has two modifications: "white" tin of 

 tetragonal crystal symmetry and specific gravity of 

 7.31, and "gray" tin of cubic symmetry and specific 

 gravity of 5.75 (Lange, 1961). Below a temperature 

 of 13.2°C, white tin changes to gray tin and crum- 

 bles to a powdery mass. Alloying tin with any other 

 metal prevents this change from white to gray tin ; 

 hence, tin is seldom if ever used in pure elemental 

 form. Tin is nontoxic, is easily melted, and has a 

 low coefficient of friction. Although tin metal is 

 soluble in strong acids, tin as plating is rendered 



U.S. GEOL. SURVEY PROF. PAPER 820 



637 



