Besides the river mentioned, the majority of those which have their sources in the mountains of Luquillo are more or less auriferous.  These are:  the Rio Prieto, the Fajardo, the Espiritu Santo, the Rio Grande, and, especially, the Mameyes.  The river Loiza also contains gold, but, judging from the traces of diggings still here and there visible along the beds of the Mavilla, the Sibuco, the Congo, the Rio Negro, and Carozal, in the north, it would seem that these rivers and their affluents produced the coveted metal in largest quantities.  The Duey, the Yauco, and the Oromico, or Hormigueros, on the south coast are supposed to be auriferous also, but do not seem to have been worked.

The metal was and is still found in seed-shaped grains, sometimes of the weight of 2 or 3 pesos.  Tradition speaks of a nugget found in the Fajardo river weighing 4 ounces, and of another found in an affluent of the Congo of 1 pound in weight.

Silver.—­In 1538 the crown officers in San Juan wrote to the Home Government:  " ...  The gold is diminishing.  Several veins of lead ore have been discovered, from which some silver has been extracted.  The search would continue if the concession to work these veins were given for ten years, with 1.20 or 1.15 royalty.”  On March 29th of the following year the same officers reported:  " ...  Respecting the silver ores discovered, we have smolten some, but no one here knows how to do it.  Veins of this ore have been discovered in many parts of the island, but nobody works them.  We are waiting for some one to come who knows how to smelt them.”

The following extract from the memoirs and documents left by Juan Bautista Munoz, gives the value in “gold pesos"[84] of the bullion and pearls, corresponding to the king’s one-fifth share of the total produce remitted to Spain from this island from the year 1509 to 1536: 

In 1509, gold pesos   8,975
1510,     "          2,645
1511,     "         10,000
1512,     "          3,043
1513,     "         27,291
1514,     "         18,000
1515,     "         17,000
1516,     "         11,490
1517-18,  "         38,497
1519,     "         10,000
1520,     "         35,733
In 1521,     "         10,000
1522,     "          7,979
1523-29,  "         40,000
1530,     "         12,440
1531,     "          6,500
1532,     "          9,000
1533,     "          4,000
1534,     "          8,500
1535,     "          1,848
1536,     "         10,000
______
Total, 15 share   277,941

The entire output for this period was 1,389,705 gold pesos, or $4,169,115 Spanish coin of to-day, as the total produce in gold and pearls of the island of San Juan de Puerto Rico during the first twenty-seven years of its occupation by the Spaniards.

FOOTNOTES: 

[Footnote 84:  Washington Irving estimates the value of the “gold peso” of the sixteenth century at $3 Spanish money of our day.]