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Application of Ground Penetrating Radar (GPR) at the Cryo-Genie Gem Pegmatite Mine, San Diego County, California Jeffrey E. Patterson University of Calgary Discovery of a major gem tourmaline pocket at the Cryo-Genie Pegmatite Mine, San Diego County, in September, 2001, prompted the author to suggest to the mine owner that Ground Penetrating Radar (GPR) might be a useful tool to assist in the exploration efforts at the mine, (Kampf, et.al., 2003, Figure
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  Application of Ground Penetrating Radar (GPR) at the Cryo-Genie Gem Pegmatite Mine, San Diego County, California Jeffrey E. Patterson University of Calgary Discovery of a major gem tourmaline pocket at the Cryo-Genie Pegmatite Mine, San Diego County, in September, 2001, prompted the author to suggest to the mine owner that Ground Penetrating Radar ( GPR  ) might be a useful tool to assist in the exploration efforts at the mine, (Kampf, et.al., 2003, Figure 1). Previous investigations at other San Diego County gem pegmatite mines demonstrated the efficacy of GPR for delineating pegmatite orientation and finding gem  pockets, (Patterson, 1996, Patterson & Cook, 1999, 2002). However, not all gem pegmatites are amenable to the use of GPR  , (Lees, pc, 2003). High clay contents in the overburden and wet clay seams within a dyke limits the depth of penetration and reduces the GPR   signal quality. Poor understanding of the mineralization sequence and internal structure of a pegmatite hampers interpretation. Therefore, this study was undertaken to establish whether GPR   would be as effective a geophysical exploration tool at the Cryo-Genie Pegmatite Mine as it has been at other San Diego County mines. Figure 1 : Gemmy Elbaite Tourmaline from the Big Monday Pocket, Cryo-Genie Mine. (Gochenour’s Minerals showcase, Mineral Society of Southern California Show, December, 2001)   2 The Cryo-Genie Mine is located in northern San Diego County, about 2 miles North-  Northwest of the village of Warner Springs, (  Agua Caliente ), (Figure 2). The locale was mentioned in the first geologic investigation of San Diego County by Blake, as part of the railroad surveys near the 32 nd  parallel, (Parke, 1854-1855). Blake reports lithia mica in the sediments of the canyon near  Agua Caliente , (Figure 4). This particular site was first prospected as the Lost Valley Truck Trail Prospect in 1904 for gem tourmaline and beryl by Bert Simmons with little success, (Gochenour, 2002). The claim was located as the Lindy B Mine by the San Diego Mineral and Gem Society in 1962 and as the Cryo-Genie in 1974 by Bart Cannon. Since 1994, Dana Gochenour has held the claim to the mine. A complete history of the current mining operations and mineralogy is given in Kampf, et.al., (2003), and at the Cryo-Genie Website at: (http://home.earthlink.net/~goke/Cryo-Genie.htm) . A mining diary of activities in 2002 can also be found on the MSA Pegmatite Interest Group website at: (http://www.minsocam.org/MSA/Special/Pig/PIG_articles/PIG_articles.html   ). Figure 2 : Site Location Map  Basic information on the geology and mineralogy of the pegmatite is available in Weber, (1963, p. 106). He describes the location, geology, and mineralization as follows: “ Deposit consists of a granite pegmatite dike, enclosed in hybrid rocks, which is exposed just southwest of the crest of a small hill. The dike strikes northward, dips about 30 degrees to the east, is about 10 ft. thick, and can be traced laterally for about 200 ft. The dike can be divided into 3 zones: (1) a lower zone, about 4 to 5 feet thick, which is chiefly graphic granite; (2) a core, about 1 ft. thick, which is composed of quartz, albite (including variety Clevelandite), muscovite, lepidolite, tourmaline, garnet, and allanite; and (3) an upper zone, 4 to 5 ft. thick, which is medium to coarse grained graphic granite with muscovite and black tourmaline crystals as long as 9 in. The tourmaline crystals of the core commonly range in color from solid black to crystals with black cores and grass green exteriors. Also noted were pale blue, pale pink, and colorless crystals. Pale crystals are thin and probably average less than ½ to 1 in. in length. Some of the smallest crystals are gemmy”. (Figure 3)     3  Figure 3 : Outcrop southwest of crest of small hill. The dyke strikes north and dips both west and east. Green and Pink Elbaite Tourmaline and Morganite Beryl were recovered from this section of Dyke 2. During October, 2001, the author visited the site to conduct a geological reconnaissance of the underground workings with a lighted display of the First Pocket, a major Quartz and Lepidolite zone. We also wanted to review the general geology as presented during a Smithsonian Museum Pegmatite Camp, June, 1997, because in 1997, the site was overgrown with brush and only small typical Orthoclase, Quartz, Muscovite, and Schorl blocks were visible on the dump of Dyke 1. Dyke 1, containing the primary mine workings, generally strikes North, dipping 26 to 36 degrees to the West. Underground, in the recently excavated stopes, the dip is West 36º. In the region of the current working face, File 104, the dip is West 26º. A typical surface exposure of Dyke 1 is shown in Figure 5. For the most part, the dyke resembles the other classic LCT, ( Č erný, 1982), pegmatites of San Diego County. But, there are significant differences that make the Cryo-Genie pegmatite unique. These differences will be discussed below. Two other dykes outcrop on the claim. Dyke 2 has been mined, in the southwest outcrop, for gem tourmaline and morganite. Dyke 3 has only been exposed in a small glory hole and appears to be barren. The preliminary investigation of Dyke 1 was conducted on 6 January, 2002. Data were collected with a GSSI SIR-4400R GPR   unit and recorded on a model SR-8100H Graphic Recorder, (Figure 7). The antenna used was a GSSI Model 3105, operating at a central frequency of 300 MHz, (Figure 6). This equipment was manufactured in 1984 and uses Intel-286 processor technology. Hardcopy, analogue, output is available on heat sensitive carbon paper. The Model SIR-4400R has limited data acquisition capability, being used srcinally for the identification of very near surface, (10 to 50 cm), concrete reinforcing rods and conduit. The maximum scan range is 400 ns. No digital signal enhancement is available on this early model. The mode of recording was ‘continuous’ for all scans.   4  Figure 4 : First geologic map of San Diego County.
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