The Acton Copper Mines, ^ 361 



opening, which is on the escarpment of the hill limestone, there 

 bending so as to dip nearly north. 



4. Theory of the Deposit. 



This may be stated as follows. Water holding sulphate of copper 

 in solution has been diffused, probably by submarinesprings, through 

 calcareous sediment, possibly containing organic matter, and the 

 salt of copper being deoxidised has been deposited in the beds 

 as sulphuret of the metal. The limestone itself holding this 

 deposit is an irregular nodular bed, the " copper limestone," of 

 the above description subordinate to the thick shale overlying the 

 great limestone of the Acton ridge. After deposition molecular 

 action has led to the formation of nodules and seofreojative veins 

 of the copper ore, and at a later period the beds have been contorted 

 and faulted, and in the fissures thus formed true veins, holding 

 copper pyrites in a matrix of calc spar and quartz, have been depo- 

 sited." 



In regard the exposures at Upton it may be remarked that 

 they seem to be the equivalent of the Acton Hill limestone, 

 and show numerous veins holding yellow pyrites, and in some 

 places galena, with calc spar and quartz. Some of these veins 

 run parallel to the strike, which is N. E. and S. W., the dip 

 being S. E., but there is another set nearly at right angles to it. 

 The true equivalent of the Acton copper limestone may be found 

 running parallel to the great limestone at some little distance. 



Since the above notes were written considerable progress has 

 been made in the work of excavation and there is still no apparent 

 diminution of the cupriferous rock — it does not appear to thin 

 out as it penetrates the strata in which it is embedded. That it 

 occurs in masses of irregular thickness along the strike of the 

 underlying limestone and thus has the character of nodular 

 matter rather than of a regular aqueous deposit is obvious. It is 

 not improbable that at the period of the infiltration of the copper, 

 disturbances and alteration of the associated strata took place to 

 a considerable extent, reducing them into their present abnormal 

 state. It is only therefore by actual experiment that the real 

 character of this cupriferous deposit can be ascertained. It may 

 underlie iu workable quantities, the whole of the space within 

 the synclinal of Acton and Upton and thus prove to be one 

 of the most extensive and valuable copper regions in the world. 

 Can. Nat. 9 No. 5, Vol. V. 



