“There is no other royal path which leads to geometry,” said Euclid to Ptolemy I.
—Proclus: Commentary on Euclid’s Elements, book ii. chap. iv.
Located in the E2 Sec. 13 T13S R4E SBM, about 2.5 miles southeast of Banner, the Royal mine workings are low on the southwest side of Rodriguez Canyon, at an elevation of 3712' AMSL. The Royal deposit has been a longtime source of lepidolite for mineral collectors. The deposit is a series of pegmatite veins between 10 and 40 feet thick, forming a stockwork averaging 10 feet in thickness, merging and layering within the top of an exposed granite knoll, and traceable for over 1500 feet along strike. The maximum surface relief is about 120 feet at a point some 400 feet east of the main workings.
The Royal pegmatite deposit was first prospected around 1902 by Bert Simmons of Oak Grove. In 1914, Frederick Merrill incorrectly reported the Royal mine location as being in Sec. 18, T. 13 S., R. 5 E. Merrill also characterized the amount of lepidolite as quite limited, and described the mine as never having been productive. At this time, the mine was said to be owned by Henry Blumenberg, Jr., of Los Angeles. In 1917, Waldemar T. Schaller reported that Simmons had obtained green tourmalines of gem quality.
In 1963, F. H. Weber described the deposit as a pegmatite dike that trends northwestward and dips gently southwest, and enclosed in Bonsall tonalite. The dike is particularly exposed along strike for several hundred feet, showing the upper and middle parts of the dike. The border zone of the upper part is said to consist of fine-grained pegmatite composed of perthite, quartz and muscovite, which grades downward into an intermediate zone of medium grained perthite, quartz, muscovite and schorl. The thickness of the upper zone ranges from 4 to 5 feet, while the middle zone of the dike averages between 1 and 2 feet thick. The middle part of the dike, or core zone, is characterized as coarse grained perthite and quartz with relatively large proportions of lepidolite, plus small amounts of grass green tourmaline, as well as pink and blue crystals occurring within the lepidolite mass, averaging less than 1 inch in length. Weber described the workings at this time as several shallow northwest trending cuts made over a distance of 100 feet along the strike of the vein. The main cut, near the middle of the workings was described as 20 feet long, 10 feet wide, and 5 feet high at the face, from which a gentle decline had been developed down dip for at least 15 feet within a lepidolite ledge.
On June 2, 1983, a claim to the deposit was made by Richard W. Olson, Byron Weege, Dave Cassianni, Richard Casey, and Otto Komarek, and named the Thursday lode in honor of the occasion. Between 1991-92, several large slabs of lepidolite were mined and manufactured into decorative tables by Harold Butler. These lepidolite tables measured up to 4 feet across by 1.5 feet thick and had polished tops. Butler also reported blue tourmaline crystals occurring as slender gem pencils up to 10 inches long.
Renewed exploration efforts began in 2003, carried out primarily by Thomas C. Hess of Murrieta, under the direction of owner Richard Casey. Work has focused on enlarging and deepening the old main cut to get below the lepidolite layer in hopes of encountering pockets of gem-quality tourmaline and related minerals. Using hand tools to extend the bottom of the cut, Hess, along with the help of others, had produced approximately 20 tons of lepidolite by August of 2007. Several solid pieces of deep purple lepidolite were recovered, some of which weighed in excess of 300 lbs. Most of the lepidolite has been well suited for lapidary uses. Associated lithia minerals include greenish blue amblygonite, and altered laths of pale pink spodumene.
References:
Bean. J. 2003. Report: A field trip to the Thursday mine (Pandora), near Banner, San Diego County, California: December.
Bureau of Land Management, 2006. Thursday Lode Claim, San Diego County, CA: Serial Number Index of Claims, United States Department of Interior; Sept.
California State Mining Bureau, 1925. Report of the State Mineralogist, Vol. 21, No. 4, p. 373.
Casey, R. 2007. Personal communication to S. L. Ritchie; regarding location and development of the Thursday lode claim; July.
Cordova, E. M. 2007. Personal communication to S. L. Ritchie; in reference to communication with Harold Butler between 1991-92; June.
Merrill, F. J. H. 1914. Geology and Mineral Resources of San Diego and Imperial Counties: Gems, Lithia Minerals. California State Mining Bureau, San Francisco, Cal. California State Printing Office, December. Chapter 1, pages 76-77.
Mudoch, J. and Webb, R. W. 1948. Minerals of California, Bulletin 136. State of California, Department of Natural Resources, Division of Mines, pages 39, 192.
Rynerson, F. J. 1967. Exploring and mining for Gems and Gold in the West. Happy Camp, California: Naturegraph Publishers, Inc.: p. 46.
Schaller, W. T. 1917. Gems and precious stones. Mineral Resources U.S., 1915, pt. 2: p. 856.
Weber, F. H. 1963. Geology and mineral resources of San Diego County, California. California Division of Mines and Geology, County Report 3: p. 188.
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Map Reference: 33°2'32"N , 116°31'10"W
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