(Hfl<;i\ ()F ORE / r,s 



telluride of tfold mid silver. >r five jr.ild in the piv-em-e of other 

 tellurides. It occurs with the auriferous silver ores and with 

 the sulphides of other metals in which the gold is present in the 

 elemental state not as a sulphide. 



I'llmary Copper Ores. Chalcopyrite, chalcocite and bornite 

 appear as primary minerals of hydatogenetic origin. The 

 native copper is either metamorphic or metasomatic in origin. 

 The chalcopyrite is by far the most important contributor to 

 the world's supply of copper, but not all chalcopyrite is primary. 

 The sulphides are derived from either acid or basic intrusives 

 and precipitated by the action H 2 S in the heated waters. 



rrimary Lead and Zinc Ores. The sulphides of lead and zinc. 

 when filling fissures, appear to be connected with acid intrusives 

 and are most abundant in the Paleozoic rock although they 

 appear in the rocks of all ages. It is from these intrusives that 

 the lead and zinc minerals appear to have been derived. 



Primary Silver Ores. True silver veins are characterized by 

 the presence of original argentiferous minerals as native silver 

 and argentiferous alloys together with the chlorides, iodides, 

 bromides, selenides, tellurides, antimonides, arsenides of silver 

 and other metals. 



In Butte, Montana, the silver seems to have been derived 

 from dikes of quartz porphyry cutting granites. At Cobalt, 

 South Lorraine and Gowganda, Ontario, the silver is derived from 

 diabase and gabbro; therefore primary silver deposits may be 

 associated with either acid or basic intrusives. 



The sulphides of the other metals also appear as primary ores, 

 when derived from some magma and precipitated by hydrogen 

 sulphide. Two carbonates appear as hydatogenetic minerals, 

 siderite and rhodochrosite; one hydrosilicate garnierite is derived 

 from a peridotite magma in its transition to serpentine and de- 

 posited in the numerous fissures by the combined action of 

 lateral secretion and hydatogenesis. 



Metasomasis. According to Le Conte, metasomasis is the 

 process by which change in the mineral composition of a rock is 

 effected. It may be produced in three ways: (1) By the alter- 

 ation of the original minerals; (2) by the replacement of the 

 original minerals; (3) by the crystallization of the minerals. 

 The three changes may be effected separately or conjointly. 



If a limestone should be replaced in part by magnesium carbon- 

 ate and therefore converted into dolomite, such adolomitization 



