36 NEW YORK STATE MUSEUM 



In this event, the precipitation as blende may be represented as 

 follows : 



ZnCO. + HoS + CaCOg = ZnS + CaCHCO^), 

 Zn(HC03), + 2U,S + 2CaC03 = ZnS + 2Ca(HC03), 



These equations are, of course, not to be taken too literally, but 

 they show how simple reactions may account for both the pre- 

 cipitation of the zinc as the relatively insoluble sulphide, and the 

 simultaneous removal of the calcite by its conversion into the 

 soluble bicarbonate of calcium, both of which operations enter into 

 the process of replacement. Thus, it is possible that, in the late 

 stages of ore deposition, carbonic acid played a role that, in the 

 earlier stages, was taken by chlorine or some other agent of similar 

 potency. At the same time, the anhydrous silicates might react as 

 follows : 



Diopside Serpentine 



SZnCOs + 3H,S + sCaMgSi.Oe = s^nS + H.Mg^Si.O, + 

 4SiO. + SCaCOs + HoO 



For an exhaustive discussion of the chemistry of natural zinc 

 solutions, Siebenthal's^ recent work should be consulted. 



In seeking zinc ore deposits, other than those of the Christiania 

 region, similar to those of the Edwards district, it is natural to 

 turn first to the very important ore bodies of Franklin Furnace, 

 X. J., which have in common with the Edwards ores their Pre- 

 cambrian age, occurrence in crystalline limestones, and association 

 with granitic intrusions. They differ from the Edwards ores, on 

 the other hand, as well as from those of all other localities, in the 

 fact that the zinc occurs in primaiy oxides and anhydrous silicates 

 and not as sulphide. 



This fact, together with the complexity of their geology and their 

 great commercial importance, makes the ores of exceptional interest 

 and has led to their repeated study by geologists ; but the problem of 

 their origin is not yet completely solved. Detailed investigation,' 

 however, has led to an explanation of the ores quite similar to the 

 one here advanced for the Edwards ores, and it is interesting to 

 note that Goldschmidt (page 252) says that the Franklin ores have 



^ Siebenthal. C. E., Origin of the Zinc and Lead Deposits of the Joplin 

 Region; U. S. G. S. Bui. 606, 191 5, p. 54. 



-Spencer, A. C, Franklin Furnace Folio, (Xo. 161), Geol. Atlas U. S., 

 U. S. G. S. 1908, p. 8. Also, The ;\Iine Hill and Sterling Hill Zinc Deposits, 

 Sussex county. Xew Jersey: Geological Surve}' of Xew Jersey, Ann. Rep't 

 of State Geologist for 190S, 1909, p. 49-52. 



