Pikes Peak

Minerals Bastnaesite, Euxenite, Monazite, quarz

A small group of pegmatites in Chaffee and Fremont Counties, Colorado, is characterized by the association of fluorite with the rare earth minerals euxenite monazite allanite, and gadolinite. The deposits, which are differentiated into central and outer zones of contrasting texture, formed chiefly during the magmatic stage. The less common minerals are the result of hydrothermal modification. Fluorite and rare earth minerals are associated in 19 of the 22 pegmatite districts in North America from which fluorite has been reported. This geochernical relationship is emphasized by the widespread occurrence of rare earth elements in fluorites.

The primary minerals of the core and the wall zone are quartz, microcline, and magnetite. The other minerals are later and form fracture fillings or replacement masses many of which are clearly related to fractures.

The sequence of veining and replacement in the wall zone appears to be:

1. Muscovite and albite

2. Purple fluorite, quartz, and chlorite

3. Specular hematite

4. Sericite

Around the margins of the core occur local concentrations of monazite, euxenite, fluorite, and plagioclase, usually in the form of one-inch to one-foot pods and clusters of crystals.

Pods of monazite and the closely associated euxenite are surrounded by aureoles of pink to dark red feldspar, a regular feature accompanying the occurrence of these minerals.

Both monazite and euxenite replace and vein the white plagioclase (calcic albite to sodic oligoclase) and are themselves veined and corroded by white fluorite, red albite, and an unidentified soft yellow-gray mineral. The monazite, which appears to be slightly older than the euxenite, is associated with a few small blebs of gadolinite and is cut by minute veinlets of apatite as well as specular hematite.

The sequence of formation of the minerals in the replacement pods appears to be as follows:

1. White albite-oligoclase, muscovite

2. Monazite and gadolinite

3. Euxenite

4. White fluorite and red albite

5. Unidentified, soft, gray mineral

6. Purple fluorite, apatite

7. Specular hematite

8. Sericite

9. Bismutite and malachite

The sequence of formation of the secondary minerals appears to be:

1. Plagioclase and minor muscovite

2. Biotite and garnet

3. Allanite, euxenite, apatite

4. Green fluorite, purple fluorite

5. Hematite

6. Sericite and vugs

7. Bismutite

8. Calcite and limonite

References

  1. http://csmsgeologypost.blogspot.cl/2013/05/rare-earth-minerals-pikes-peak-region.html

  2. http://www.minsocam.org/MSA/collectors_corner/arc/copeg.htm

  3. http://www.coloradomining.org/Content/Programs_pdf/M%20Smith.pdf

  4. https://books.google.cl/books?id=9o02AQAAMAAJ&pg=SL8-PA18&lpg=SL8-PA18&dq=pikes+peak+ree+deposits&source=bl&ots=Ob0YlcNq9n&sig=UopJjRfuHbARTSwmqvVmfC20TWs&hl=ru&sa=X&ved=0ahUKEwjl88ji2vPMAhWEiZAKHdWKCmkQ6AEIRDAG#v=onepage&q=pikes%20peak%20ree%20deposits&f=false

@ Ph.D. Natalia Petrovskaya

June, 2016

nataliapetrovsky@gmail.com