Patterns of Mn enrichment in
fine-grained apatite from the Black Mountain Pegmatite, Maine
Livingston, Kelsey M.,
and Wise, Michael, 2014, Patterns of Mn enrichment in
fine-grained apatite from the Black Mountain Pegmatite, Maine:
Geological Society of America Abstracts with Programs,
Northeastern Section - 49th Annual Meeting Lancaster, PA, (23–25
March), v. 46, no. 2. (Kutztown University advisor on the project
Friehauf, Kurt)
In the spodumene- and tourmaline-rich Black Mountain granitic
pegmatite (western Maine, USA) apatite occurs as one of three
primary phosphate minerals in this complexly zoned body. During the
examination of the pegmatite using cathodoluminescence, fine-grained
apatite was found to be widely distributed throughout the primary
zones and replacement unit of the pegmatite. Millimeter- to
micrometer-sized apatite was observed mainly disseminated in albite,
and sparingly in microcline, quartz, lithian muscovite and
montebrasite. Electron microprobe data provides evidence for the
chemical evolution of apatite with respect to Mn enrichment during
successive stages of crystallization of the pegmatite.
The Mn content of apatite from the wall zone averages 4.1 wt.% MnO.
The average Mn content of apatite during crystallization of the
subsequent 1st intermediate, 2nd intermediate, and 3rd intermediate
zones shows a steady increase of 1.5 wt.%, 2.5 wt.%, and 3.0 wt.%
MnO, respectively. Within the tourmaline-lepidolite-albite and
lepidolite-albite units of the 3rd intermediate zones, the MnO
concentration of apatite drops sharply to about 0.6 wt. %, but
increases again to nearly 2.0 wt.% in late lepidolite-bearing units.
The last major unit to crystallize, the replacement body, contains
apatite with an average MnO concentration of 1.3 wt.%, similar to
apatite found in the 1st intermediate zone of the pegmatite.
The non-linear behavior of Mn enrichment in apatite is attributed to
the mineralogy of each zone, where accessory minerals may be present
that have a higher affinity for Mn over apatite. Co-precipitation of
manganocolumbite and elbaite provides competition for Mn in the melt
and may be responsible for the sudden depletion of Mn in apatite
from the 3rd intermediate zone. The competition of ions between
different mineral phases gives insight in the fractionation patterns
on Mn in Black Mountain and provides a possible pathway to
determining the trace element chemistry throughout the evolution of
the pegmatite.
Patterns of Mn enrichment in
fine-grained apatite from the Black Mountain Pegmatite, Maine