Saturday, November 19, 2011

COLORADO AMETHYST


Wall of reclaimed Crystal Hill Mine with brecciated volcanic rock.

The Crystal Hill District is located a few miles north and west of La Garita, Colorado (western side of San Luis Basin north of Alamosa) near Carnero Creek.  The District was founded in 1881 by  prospector and mining man Mark Biedell.  The District produced native gold and silver from a collapse breccia structure for a few years before mining operations ceased, mostly by 1900. 

 Two small, short-lived mining camps sprang up in the area. The first, Biedell, appeared in 1881 and 1000 men were mining by 1883; the second sprang up in 1886 and was known as El Carnero (GeoZone, 2011).  The latter area was producing from “lead carbonate” (BLM information sign), a mineral I presume is cerussite (PbCO3).  
   
In the 1940’s mining evidently returned to Crystal Hill in the form of the Crystal Hill Mining Company (BLM information sign); however, I was unable to locate additional information about this later activity.

Voynick (1994) noted that “exploration geologists returned to crystal Hill in the late 1970’s, delineating a large, low-grade zone of disseminated gold near the top of the hill.  The Crystal Hill Mining Company developed an open-cut heap leach mine recovering 30,000 troy ounces of gold in four years”.  In2009? “stimulus funding” allowed the BLM to reclaim, at least partially, the old mine.  BLM now allows access on the reclaimed area but warns that the main pit is off limits and on private land.   
  
Rockhounds appreciate Crystal Hill for the occurrence of terminated amethyst and quartz crystals.  So, in summer 2010 I was headed to Alamosa for a BLM meeting and decided to take a side trip to Crystal Hill with my crack hammer in tow.  I found the appropriate brecciated rocks in the cliff associated with the reclaimed mine but was rather unsuccessful.  I then begin to pound on large boulders that were scattered around the area and finally was able to locate some vugs.  Many contained very nice, but rather small, slender terminated quartz crystals.  However, I did notice the telltale violet color of an amethyst crystal in one vug.  I brought the enclosing rock home and cleaned it with water, soap and muratic acid and was able to isolate a very nice crystal.

Terminated crystal of amethyst projecting from vug. 


REFERENCES CITED 

GeoZone, 2011, The Lost Mine of Saguache Creek: www.thegeozone.com/treasure/colorado/tales/co014b.jsp#prospecting

Voynick, S. M., 1994, Colorado Rockhounding: Missoula, Mountain Press Publishing Company.



 

RMFMS: A GEOLOGICAL MENAGERIE

The Rocky Mountain Federation of Mineralogical Societies (RMFMS) is perhaps the largest, in terms of land area, of any American Federation regional organization.  Member clubs are located in Arizona (16), Arkansas (1), Colorado (17), Kansas (6), Nebraska (1), New Mexico (8), North Dakota (2), Oklahoma (10), South Dakota (2), Texas (1), Utah (10), and Wyoming (4) and these states have a combined area of ~1.85 million sq. miles, about one-half of the total area of the lower 48 states.  


I have always been interested in the diverse geology and physiography displayed in RMFMS states.  There are folded and thrust faulted Ouachita Mountains in the east (Arkansas) that are related to continental plate collision (Africa and North America), a large piece of non-mountainous terrain that was once covered by Pleistocene glaciers (Kansas, Nebraska, North Dakota, South Dakota), and large basement-cored mountains in Colorado, Wyoming, Utah, New Mexico, and Arizona.  Each state has unique geological features and each offers a plethora of collecting localities.  

To read more about the physiography and geology of RMFMF states check out the November newsletter at:  www.rmfms.org 


mike