420 FERGUSON. 



These are not in the vein itself, which is largely hard massive quartz, but in 

 the decomposed andesite on the hanging wall wliere small rich stringers had 

 been followed by the early miners in irregular stopes and passages. 



The Montana vein now being prospected by the Aroroy Mining Company lies 

 on a spur extending toward the northwest from Mount Bagadilla. This vein 

 can be traced from the gorge of the Guinobatan Eiver northwesterly for a distance 

 of some 1,500 meters. It is narrower than the average for the district, varying 

 from 1 to 3 meters in thickness, and, as it is nearer the water-level, the ore is less 

 oxidized than in others. Banding is entirely lacking, the oxidized portions of 

 the ore showing irregular honeycombing. Although rich ore has been discovered 

 at various places and a line of ancient open cuts shows that the surface ores 

 were formerly worked to some extent, development has not yet proceeded far 

 enough to determine the importance of this vein. 



The deposit formerly worked by the Gold Bug Company and now being explored 

 by the Aroroy Mining Company is located on the western end of Mount Kalakbao. 

 The rock here consists of an irregular deposit of sandstone, shale, and conglo- 

 merate, apparently all derived from the andesites and pyroclastics of the Panique 

 formation, which form the mass of the moimtain. These sediments are cut here 

 by a basic dike of uncertain composition, but allied to the leucite-tephrite found 

 3 kilometers north of this dike. Small veins of blue quartz up to 1 meter in 

 width, and oxidized only to a depth of about 1 meter below the surface, also cut 

 these sediments. The shale is the lowest of the sediments and is found only near 

 tha basic dike in the Gold Bug open cut. It is nearly black and is heavily impreg- 

 nated with pyrite along its cleavage planes. Under the microscope it is seen to 

 contain numerous, fresh, angular fragments of plagioclase feldspar. It carries 

 small values in gold, probably never exceeding 4 gi'ams to the ton. The sandstone 

 and conglomerate lie above the shale and grade into each other irregularly in a 

 way to suggest stream deposition. These rocks in irregular areas along the 

 .surface contain values, and lines of old native workings are found in many places. 

 The ground was explored by the Aroroy Mining Company in a series of open cuts. 

 These show the sandstone to be deeply iron-stained and oxidized almost to the 

 consistency of clay for a depth of from 2 to 5 meters from the surface, where it 

 changes rather suddenly to a blue, but still somewhat decomposed, rock more or 

 less impregnated with pyrite. Values of 30 grams and over per ton are often 

 obtained in the shallow oxidized zone, but where the color changes to blue and 

 the rock becomes firmer, the values soon sink to 5 grams or less. Apparently, 

 the whole deposit is the result of filling of the open spaces of the sandstone by 

 mineralizing solutions and in the oxidized zone this has been greatly enriched 

 by residual concentration. 



The El Sol vein occurs farther east on Kalakbao Hill. This consists of iron- 

 stained quartz, partly honeycombed but not banded, which may be the continuation 

 of the IMontana vein. Eich ore has been found in places, but at the time of my 

 last visit no great amount of development work had been done. The southeastern 

 extension of this vein is cut off by the Pirate vein extending nearly east and west, 

 one of the few in the district which do not follow the northwesterly strike. 



The Sj-ndicate ilining Company is working a group of claims on the central 

 part of Kalakbao Hill. 



The principal vein is known as the Nancy No. 1, and shows a width of 16 

 meters although not all in workable ore. The ore shows well-defined banding near 

 the footwall, and is much broken and oxidized in the central and hanging wall 

 portions. In the lower levels calcite forms a small proportion of the gangue. 

 The assays show extremely irregular values, but the greater part of the richer 



