116 PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
it would probably not pay to save as scrap mica the muscovite. obtained in the feldspar mining. No plate mica was observed.
Biotite
is moderately abundant in certain parts of the pegmatite. It penetrates
the feldspar and quartz in lath-shaped masses, the largest of which was
2 yards long by 3 inches wide and one-fourth inch thick.
As
in most other feldspar quarries, small garnets are abundant only in
certain portions of the deposit, the coarser graphic granite and the
pure feldspar being almost entirely free from them, and they are not
seriously injurious to the commercial value of the deposit.
Cavities
up to 1 foot in diameter and of various form are rather a constant
feature of the coarser portions of the pegmatite in the northern part
of the quarry. They may occur within the areas of pure quartz or
feldspar, on the border between quartz and feldspar masses, or more
rarely in the coarse graphic granite. Usually they contain groups of
somewhat smoky semitransparent quartz crystals, some of which make
handsome cabinet specimens. In a few, transparent green tourmalines and
aquamarines (beryl) of gem quality have been found.
The
schists and gneisses which border the pegmatite-are exposed at the
southern end of the quarry, where they show evidence of much softening
as a result of the pegmatite intrusion. In general they are rather flat
lying. Probably the pegmatite mass is also in general somewhat flat
lying, though very irregular. It is probable that the workable
pegmatite does not extend southward much beyond the limits of the
present pit, but northward it is known to extend into property said to
be controlled by the Maine Feldspar Company. Here it has been worked in
the past from a number of small openings and very considerable amounts
of commercial spar are still available.
The
methods of operation at this quarry are somewhat antiquated for a
working of this size, the drilling all being done by hand and the
blasting by black powder. A tramway carries the waste to dump piles and
the good rock to stock sheds, from which it is loaded into wagons and
hauled 1-3/4 miles to the mill near Cathance station (p. 18).
North Topsham feldspar quarry.—A
feldspar quarry in the northern part of the town of Topsham, one-half
mile west of Cathance River and 1 mile south of the Topsham-Bowdoinham
line, was formerly operated by the Trenton Flint and Spar Company, the
rock being hauled by team 2 miles to the mill near Cathance station.
The quafry is located on the western valley slope of the river and is
an irregular opening extending north and south along the hill slope for
about 200 feet and extending into the hill for about 40 feet. There is
a complete absence of any regularity in the arrangements of the
pegmatite constituents.
