quartz,
and silicified andesite. The gold is usually about 50 per cent free
nulling. It is also included in pvrite and occurs rarely as gold-silver
telluride. The ore is not usually of high grade. The Bua and the
Consolidated mines are the most extensively operated, and each is
equipped with a modern free-discharge stamp mill and cyanide plant. The
Camote, Headwaters, and Kelley mines are also developed, the first two
of which are equipped with plants. The Arroroy district in the
northeastern part of the island of Masbate, which has undoubtedly
produced much gold in the past from placers and shallow workings, has
been described in some detail by Ferguson.1 The oldest rocks
are slates of undetermined age, intruded by diorite and more basic
plutonic rocks, and associated with later volcanics, chiefly augite
andesite, and more basic rocks. Remnants of dark-blue limestone of the
middle Tertiary are found. The majority of the veins strike northwest
along tectonic lines. The veins are confined to the igneous rocks and
are, as a rule, wide and regular. The primary ore is chiefly gold,
associated with pyrites in a quartz-calcite gangue, but the veins have
been oxidized to considerable depths and the altered upper portions
only have been mainly developed to date. Production from Arroroy has
been relatively small in recent years, pending development work, but
the largest mill in the Philippines was in course of erection and was
expected to be completed in 1911 for the Colorado group. Dredging has
been tried on the streams of this district, but has failed to prove
profitable to date. The Paracale district, in Ambos Camarines, on the
Pacific coast of Luzon, has been an important producer of gold in early
times from placers and shallow workings, and has been the scene of
considerable dredging activity and some underground exploration work of
recent years. There are now three dredges in the district, and one
modern 20-stamp mill has been recently put up. The dredging field is
important, though heavy vegetation, sticky bottom clays, and much black
sand offer difficulties. The rocks of the district are mainly
regionally metamorphosed sandstones, shales, and intruded granite,
together with basaltic and andesitic flows and dikes. Two properties
have been chiefly developed, one with a calcite stringer lode carrying
sulphides, tellurides, and free gold, and the other with a wider vein
carrying copper sulphides and gold in a quartz gangue. The production
of the last few years has been almost wholly from placers and mainly
from dredging.
NUMBER OF PRODUCING MINES.
The
following table indicates the number of mines producing gold and silver
in 1910, divided into placers and deep mines. The placers are those in
which gold, the silver in natural alloy with the gold, and in a few
instances platinum, are recovered from gravels and sands whether by
hand washing, sluicing, "hydraulicking," drifting (in frozen ground or
ancient buried river channels), or dredging. The deep mines are those
producing gold and silver mainly from underground workings, including
those whose ores are valuable chiefly for copper, lead, or zinc, but
which contribute precious metals as by-products. In addition to the
producing mines here enumerated, many mines were being prospected and
developed without making
1
Ferguson, TT. O,, The Arroroy mining district: Mineral Resources of the
Philippine Islands, Bureau of Science, Manila, 1910, pp. 18-25.
