622 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.45. 



ever, the ore itself has been dynamically metamorphosed, the sulphide 

 mass (excepting the pyi-ite which, being too hard, has suffered shat- 

 tering only) having flowed like " thick muck. " 



Huelva, Spain} — The greatest single copper-producing district 

 abroad, ranking fourth among those of the world, occupies an east- 

 west mineralized zone, lying mainly in the Province of Huelva, 

 southern Spain, and including the well-known deposits at Tharsis 

 and Rio Tin to. The ore is massive, homogenous pyrite, carrying 

 chalcopyrite and subordinate associated galena and sphalerite, with 

 local enrichments of chalcocite and minor bornite. The ore-bodies are 

 lenticular masses, many in number and ranging up to enormous sizes 

 (largest about 3,000 by 600 by 1,500 feet) and are mainly inclosed 

 within those portions of Paleozoic slates and intrusive porphyries that 

 have suffered severe dynamic metamorphism and been converted 

 into schists (chiefly sericitic). The ore bodies are in proximity to ex- 

 tensive intrusions of acid and basic igneous rocks, showing advanced 

 differentiation, and are usually located along lines of more or less fault 

 movement. Microscopic examination of the ores by Finlayson 

 results in the following conclusions i^ (1) The copper occurs as a 

 definite mineral in the ore and is not chemically combined with the 

 pyrite. (2) The primary mmerals have deposited in the foUowing 

 order: pyrite, chalcopyrite, sphalerite, galena. (3) The ore bodies 

 have been secondarily enriched; in the lean deep ores chiefly by a 

 change of chalcopyrite to chalcocite, and in the richer, or shallower 

 ores, chiefly by a deposition of chalcopyrite followed by chalcocite. 

 Bornite occurs in very subordinate amounts, and appears interme- 

 diate in formation between chalcopyrite and chalcocite. (4) The 

 only primary copper mineral is judged to be chalcopyrite; the other 

 copper minerals appear to have resulted from descending solutions. 



The deposits are conceived by Finlayson to be due to the replace- 

 ment of altered rocks by solution, rising along structural planes of 

 maximum permeability, and originating through concentration by 

 border segregation in deep-seated igneous rocks prior to their final 

 intrusion and consolidation. 



Shasta County, California.^ — The deposits of this important copper 

 district comprise numerous and extensive lenses of cupriferous pyrite 

 inclosed within mashed alaskite-porphyry, which near the ore bodies 

 is practically a schist, containing considerable sericite (with parago- 

 nite) and chlorite. The ore, which averages 3 to 3^ per cent copper, 

 is pyrite with chalcopyrite and subordinate sphalerite and in less 

 amounts still, galena, bornite, and chalcocite; the gangue is quartz, 

 calcite, and barite. The deposition is attributed to replacement of 

 the schistose rock by solutions, expelled from nearby igneous rocks 



1 Finlayson, The pyritic deposits of Huelva, Spain. Econ. Geol., vol. 5, 1910, pp. 356-372 and 403-437. 



2 Idem , p. 420. 



8 Graton, Bull. 430, U. S. Geol. Survey, 1910, pp. 71-111. 



