ART. 2. 



PETEOLOGY AT GOOSE CREEK SHANNON. 



83 



The sulphides, which include galena, chalcopyrite, and sphalerite, 

 are of uncertain position and are not included in the above table. 

 Galena was observed included in, and apparently contemporaneous 

 with, chlorite, prehnite, and apophyllite, which would seem to indi- 

 cate that it was deposited at three different times. Chalcopyrite 

 was found included in prehnite and apophylhte, and sphalerite in 

 apophyllite. 



ORIGIN OF THE ZEOLITES AND 

 ASSOCIATED MINERALS. 



There is a continuous sequence of 

 events from the close of the mag- 

 matic period, marked by consolida- 

 tion of albitic rocks, and the dep- 

 osition of the zeolites. Where the 

 solutions were confined at the final 

 consolidation the albite rocks contain 

 miarolitic cavities in which were de- 

 posited, in addition to the lining of 

 quartz and albite, diopside, chalcopy- 

 rite, byssolitic hornblende, epidote, 

 and chlorite. Moreover, the reac- 

 tions of these solutions on the adja- 

 cent pegmatites produced, in the 

 first stage, diopside from augite, 

 albite from plagioclase, and titanite 

 by the replacement of magnetite. At 

 a later stage the diopside was re- 

 placed by fibrous hornblende. 



In the most common type of 

 hydrothermal alteration along the 

 diopsidizing seams, the reactions of 

 the solutions upon the previously 

 consolidated normal diabase forming 

 the walls of the crack are the same, 

 namely, albitization of the plagio- 

 clase, followed by sericitization, 

 diopsidization of the augite and replacement of the magnetite by 

 titanite. In the open space of the central crack the minerals de- 

 posited were diopside with less chlorite and titanite and, rarely, 

 axinite. 



No definite line can be drawn separating the thin seams accom- 

 panied by hydrothermal alteration, from the miarolitic cavities on 

 the one hand and from the zeolite bearmg veins on the other. The 



Fig. 31.— Calcite showing the common- 

 est HABIT OF AMBER COLORED CALCITE 

 OCCURRING IN THE VEINS. 



