According to an estimate of the Bureau of Science, there are in all 800 to 1,000 square kilometers of placer grounds in the Philippines still undeveloped. The production of gold in 1916 was 2,265,789 fine grams, worth ₱3,011,755; in 1918 the production was 1,937,941 fine grams valued ₱2,575,970.
Silver.—Silver is found alloyed with the gold in all of the gold deposits in the ratio of 1 to 4. No attempt has as yet been made to develop the silver mines of the islands. There is no doubt, however, that the silver deposits can be advantageously developed on a commercial basis because the supply of silver in the world is declining and because the neighboring countries, such as China and Japan, are on the silver standard basis.
Iron.—Valuable deposits of high grade iron ores are found in the eastern and southeastern cordilleras of Luzon. Extensive deposits are available in Bulacan, Rizal, Camarines, and Surigao. The Surigao field has a total area of 100 square kilometers with an average depth of 3 meters. The total estimated iron-ore deposit is about 500,000,000 tons. This region is accessible from the coast. The Bulacan deposit contains approximately 1,200,000 tons of ore. No survey has been made of other fields, but it is estimated that at least another 500,000,000 tons of ore are dormant in them. If properly developed, these deposits would yield sufficient ore to meet the local needs for iron and steel products, perhaps with a surplus for exportation. As a result of the economic development of the country, the importation of iron and steel and their manufactures has shown an annual tendency to increase, as may be seen from the following figures:
Importation of iron and steel and manufactures thereof
| Year | |
| 1910 | ₱11,118,916 |
| 1913 | 17,227,808 |
| 1918 | 24,507,970 |
| 1919 | 44,735,174 |
| 1920 | 43,759,204 |
| 1921 | 43,529,079 |
| 1922 | 15,208,761 |
The demand for iron and steel goods in the Philippines is bound to remain on the ascendant with the daily increase in the use of structural iron and steel for Government buildings as well as for private structures. Here again is another vast field awaiting exploitation by enterprising men and capital.
Manganese.—Manganese deposits are found in Ilocos Norte, Pangasinan, Bulacan, Tarlac, Masbate, and Benguet. Little, if anything, seems to have been done in the way of developing them. This mineral product is of great industrial value and has a sure demand on the world’s market. The United States in 1914 imported 288,306 tons of this product, and in 1917, 656,088 tons, valued at ₱21,000,000.
Coal.—No other mineral deposits are as widely scattered in almost every island of the Archipelago as coal. Extensive deposits which would warrant investments of capital are found in Cebu, Polillo, Mindanao, Masbate, and Mindoro. According to estimates made by the Bureau of Science the probable minimum tonnage of the different grades of coal found in this country is about 68,000,000 metric tons. Tests made by the same bureau show the following figures on the comparative calorific value of imported and local coal:
Calorific values of various coals
| Source of sample | Calories |
| Australia | 6,614–6,987 |
| Japan | 6,691–7,127 |
| Borneo | 6,664 |
| Philippines: | |
| Bataan | 4,753 |
| Uling, Cebu | 6,733 |
| Polillo | 5,925 |
| Negros | 4,402 |
| Zamboanga | 6,427 |
| Laguna | 4,510 |
| Butong | 7,779 |