General comments 251
The Franklin zinc deposit 251
Historical observations 251
General geologic relations 253
Dikes 253
Pegmatites 255
Potassic pegmatites 255
Contact relations for potassic pegmatites
256
Sodic pegmatites 257
Designations on mine maps 257
External morphology of the Franklin orebody
258
Dimensions 259
Internal structure and composition 259
Structure 259
The zinc ore units 260
The calcium silicate units 262
The Sterling Hill zinc deposit 263
Historical observations 263
General geologic relations 263
External morphology 264
General configuration 264
The keel 264
The east limb 264
The west limb 264
The cross-member 266
Dimensions 266
Internal structure 266
General relations 266
Faulting 267
The sinking hypothesis 267
Internal zoning 268
Outer zincite zone 268
Central zincite zone 268
Black willemite zone 268
Brown willemite zone 269
Pyroxene zones 269
Franklinite zone 269
Gneiss zone 269
Special features 269
Rubble breccia 269
Saprolite - the mud zone 269
Saprolite - the Sterling depression 271
Comparisons of the Franklin and Sterling
Hill deposits 271
Similarities 271
Differences 271
Relations to nearby formations 272
Physical linkage hypotheses 272
The Langban Mine near Filipstad, Sweden 272
The origins of the deposits 273
Introduction 273
Theories of origin 274
Early observations and hypotheses 274
Recent studies 276
Models of the ore deposits 278