IX, A, 3 Dalburg and Pratt: Iron Ores of Bulacan 235 



creases in the dip of the dip needle were often obtained near 

 outcrops, but quite without regularity, so that when plotted up 

 according to approved methods they yielded no intelligible data. 

 At distances of from 30 to 50 meters from the outcrops the 

 deflection of the horizontal needle is almost normal or, more 

 accurately, it is uniformly about 3° east, while the normal deflec- 

 tion in the Philippines is about 1° east. If the results of the 

 magnetic survey alone are considered, the conclusion to be 

 drawn is that large bodies of hematite or magnetite do not exist 

 in the region. But if the other data presented herewith be 

 considered, it appears that the quantity of ore is large enough 

 to be of economic importance. 



If the ores originated in the manner suggested by this 

 geologic study, it is probable that they persist for a reason- 

 able distance below the surface, since the dip or pitch dimen- 

 sion of a replacement or vein deposit which has been formed 

 under magmatic influences, as these ores probably have, would 

 presumably be of the same order of magnitude as the strike 

 dimension of the same deposit. To assume that such a propor- 

 tion exists in estimating ore reserves, however, would not be 

 justified without more evidence than is available for the Bulacan 

 ores. On the other hand, the vertical extent of the ore bodies 

 in the present case ought surely to be as great as their least hori- 

 zontal dimension, that is, their width, and in order to obtain 

 some basis of estimation it will be assumed that such is the case. 



Judging solely by the extent of the outcrops, it appears that 

 the Camaching ore body contains a much larger tonnage than 

 all the other deposits. The outcrop at Camaching is 600 meters 

 long, and measured widths varied from 20 to 70 meters. The 

 average specific gravity of the ore was determined as 4.7 ; taking 

 20 meters for the average width of the deposit over the length 

 of the outcrop and assuming that the ore will continue in depth 

 a distance equal to its least surface dimension, there results from 

 calculation something over 1,100,000 tons as the estimated ore 

 reserve at Camaching. 



In view of the conservative figure used for the average width 

 and for the extent of the ore below the surface, it appears that 

 the tonnage obtained represents the minimum quantity of ore 

 available rather than the probable size of the ore body; that is 

 to say, there is present at least this quantity of ore. 



Employing similarly conservative figures for the other ore 

 bodies, there results a combined total of about 100,000 tons of ore. 

 Indeed, only at Hison and Santa Lutgarda can one be definitely 



