MINERAL RESOURCES OF AROROY DISTRICT. 419 



is another feature which can not satisfactorily be explained at j^resent. 

 Possibly the lenses of manganese ore, present in the slates of the Kaal for- 

 mation, are of earlier origin than the veins, and the ascending solutions 

 following fissures cutting through these bodies brought up the manganese 

 oxide, while others not so situated are lacking in this constituent, or 

 it may be that the different types of veins are indicative of different 

 periods of mineralization. 



The gold is only about 25 per cent free milling, apparently due to the 

 manganese oxide and, although alloyed up to 10 or 20 per cent by weight 

 with silver, contains practically no copper, and the ore is well suited to 

 cyanide treatment. 



Individual properties. — It is my purpose to give short notes on the 

 properties which at the time of my last visit were furthest developed. 

 The fact that many are omitted is no evidence that they may not be 

 as fully wortJiy of consideration as their more developed neighbors, 

 but in a region where work is progressing so rapidh' as in the Aroroy 

 district to-day, it would serve no good purpose to multiply descriptions 

 which rapid development is rendering obsolete. 



The Keystone Mining Company has developed one vein on Aroroy Mountain 

 by means of two shafts 85 meters apart and connected by a drift at the 20-meter 

 level sunk on the vein at the top of the hill. The deeper shaft now reaches a 

 depth of 42 meters. The ore differs from the type commonly met with in that 

 there is a far smaller amount of manganese present than in other veins of the 

 district, and the characteristic banding observed elsewhere is lacking. The ore 

 is a white quartz, stained red with iron oxide and to some extent honeycombed. 

 The quartz is much shattered and shows subsequent mineralization in the shape 

 of many small quartz stringers cutting the vein in all directions. The ore is 

 oxidized throughout to the bottom of the shaft ; however, the larger pieces of 

 quartz often show cores of the characteristic bluish quartz carrying a considerable 

 proportion of pyrite. 



The Colorado Mining Company controls a group of claims on ]\Iount Baga- 

 dilla. The veins outcrop on this property, the best developed of which is known 

 as the "No. 5." This has been opened by drifts at elevations of 230 meters and 

 290 meters above sea-level, connected by an incline shaft in the footwall, and 

 winzes sunk to a depth of 50 meters below the lower level. This vein, which is 

 about 5 meters in width, shows the most beautifully marked banding of any in 

 the district, particularly near the footwall. The values run rather irregularly, 

 but a fairly well defined pay streak of about 2.5 meters width on the footwall 

 side, although generally separated from the footwall by 0.5 meter or less of 

 lower grade material, carries the richer part of the ore. On the hanging wall side 

 the decomposed andesite carries values for about 1 meter from the wall of the 

 vein, these probably being contained in small quartz stringers which are found 

 near the vein. A curious feature is that the vein makes a sharp turn toward 

 thv3 northeast at a considerable distance from the portal of the adit, its normal 

 course being northwest. It follows this new direction for about 8 meters and 

 then resumes its northwesterly course, apparently due to a pre-existing north- 

 easterly fault. 



Another vein on the Buena Suerte claim of the Colorado Company's property, 

 to the southwest of "No. 4", shows ancient workings of considerable extent. 



