X, A, 5 Pratt and Lednicky: Iron Ore in Surigao 339 



Point, and the line of contact between them and the ore deposit 

 runs south-southest. Blocks of limestone are found resting on 

 the ore formation on the hill southwest of Capandan. Judging 

 from the character of this limestone, the sedimentaries are prob- 

 ably of Miocene age. An escarpment marks the edge of the 

 sedimentaries and forms a prominent line of hills trending 

 south-southeast back of Capandan. The sedimentary rocks ap- 

 pear on the coast on the southern edge of the ore deposit in the 

 ridge at Carrascal, the line dividing them from the ore deposit 

 passing westward beyond Mount Legaspi. Thus the heavy, 

 broken line which delimits the ore deposit in Plate I marks, also, 

 the line of contact between sedimentary and igneous rocks 

 throughout most of its course. The line approaches more closely 

 to the summit of Mount Legaspi, however, than do the sedimen- 

 taries to the west, because the upper slopes of this peak show 

 very little ore. It recurves, also, at its southern extremity to 

 separate the area of alluvium around Carrascal Bay from the 

 iron-ore formation. The numerous small islands which lie off 

 the coast between Capandan and Carrascal are all composed of 

 sedimentary rocks, except Ludguron Island in Carrascal Bay, 

 which is partly covered with iron ore. 



CHARACTER OF THE IRON ORE 



The ore is principally ferruginous clay, but contains also an 

 abundance of small, round pellets of hydrous iron oxides, as 

 well as fragments or crusts of the parent rock, much altered, 

 porous, and iron-stained, but maintaining their original form. 

 Mineralogically the ore is probably a series of hydrous iron 

 oxides related to limonite. The surface of the deposit is a deep 

 reddish brown, almost crimson at places, but beneath the surface 

 the color is lighter — a yellowish brown — while the transition 

 stage between the ore and the underlying rock is pale green. 

 The thickness of the mantle of ore varies irregularly up to a 

 maximum of about 20 meters. The ore in place is soft and very 

 spongy or mealy. In walking over it one often breaks through 

 the crust into small openings or cavities beneath the surface. 



The iron ores of the Nipe Bay region in Cuba appear to be 

 similar in every respect to the iron ore in Surigao, and the 

 reader who desires more detailed information will find elaborate 

 descriptions of the Cuban ores with studies of the various steps 

 in the alteration processes from serpentine to hydrous iron 

 oxides.^ 



" The Mayari Iron-Ore Deposits, Cuba, by James F. Kemp, is especially 

 good. Bull. Trans. Am. Inst. Min. Eng. (1915), 98, 129. 



