Esmeralda Mine, Mesa Grande, Mesa Grande Mining District, San Diego County, California, USAi

Regional Level Types
Esmeralda Mine	Mine
Mesa Grande	- not defined -
Mesa Grande Mining District	Mining District
San Diego County	County
California	State
USA	Country

"Esmeralda"
—Spanish, meaning "Emerald".

Setting:
The Esmeralda is a gemstone mine located in the E2 NE4 SW4 Sec. 13, T11S, R1E, and the W2 NW4 SW4 Sec. 18, T11S, R2E, SBM, approximately 1.24 miles (2 km) west of the Himalaya mine group of claims; situated along a ridge east of Temescal Canyon, approximately 4.1 miles (6.6 km) northwest of Mesa Grande. The property consists of a patented lode mining claim containing an area of 15.34 acres, which encompasses a large gem-and-rare earth element (REE)-bearing pegmatite deposit developed by surface and underground workings.

History:
The Esmeralda was discovered and claimed by Gail Lewis in 1899, and subsequently relocated and further prospected by Arthur L. Watkins, up until sometime around 1903.^[1][2] Harry E. Dougherty and J. D. Stone, both of Mesa Grande, had staked a claim to the deposit on May 3rd of 1904. Together they organized the Native Gem Mining Company, and began serious development of the deposit. Kunz described the work in 1905 as two open cuts made across the vein, extending to a depth of 7.5 feet; and a single tunnel which had tapped the ledge at a point some 28 feet below the surface. The pockets were described as quite large, containing quartz crystals, orthoclase, and albite in beautiful transparent crystallizations. Lepidolite, in pieces weighing from 50 to 300 pounds were noted to occur in conjunction with the pocket material. Gem tourmaline was recovered in colors of pink, red, purple, blue, and greenish blue to green. Pink beryl, aquamarine, and golden beryl were also reported. About $300 was expended, producing about 20 pounds of gem-quality tourmaline. Operations continued intermittently up until the mine was patented on November 12th of 1908, but work had reportedly ceased around 1909.

In 1956, John Sinkankas began exploring the deposit with renewed hardrock mining. The old tunnel described by Kunz in 1905 was converted into a permanent explosives magazine, and was secured by a sturdy wooden door. Drilling, blasting, and mucking by hand, the main open cuts were expanded and deepened, and became passionately referred to as the "glory hole" workings. By mid 1957, the mine had been purchased by Peter Martin of San Diego, who also located additional mining claims which bordered the mineral patent. Between 1960 and 1964, several roadway and exploratory cuts were made along the deposit and adjacent mining claims by Martin using a small track-type dozer. Sinkankas, together with Josie Scripps, Robert Coates, and several local miners, continued following the paystreak by vigorously blasting along the main cuts, which ultimately extended the glory hole workings to a depth of approximately 40 feet below the original surface exposure. Several underground drifts were also driven to append the glory hole workings.^[3]

The property was acquired by Pala International of Fallbrook, California, on August 9th, 2011 - under a joint venture with RPL Mining Limited LLC, based in Delaware. Preparation of the site for renewed underground exploration was underway by the spring of 2012. Day to day operations will be conducted under the direction of Benjamin Castillo Meza.

Geology:
The Esmeralda deposit was described in detail by Richard H. Jahns in 1957, and summarized by F. H. Weber in 1963. The pegmatite dikes in the mine area occur in medium- to coarse-grained gabbroic rocks. The main dike, which is broadly sinuous, ranges in thickness from 2 feet to nearly 40 feet in the mine area, and is locally very irregular in detail. It trends north-northwest and dips steeply west-northwest in the vicinity of the southern group of workings where it splits into several sub-parallel branches.

The principal rock type in all of the dikes is graphic granite which contains scattered, but locally abundant albite, muscovite, and quartz. In most places it forms almost the entire thickness of the dikes. Only in the thickest parts of the main dike are other types of pegmatite prominent. The core of this dike is exposed only in the underground workings beneath the main cuts. Most of it has been mined out, but evidently it formed an irregular mass with a 40 degree to 60 degree south-southwest plunge. In horizontal section its maximum dimensions were about 3 feet by 25 feet, and it appears to have been about 25 feet long, as measured in a down-plunge direction. The core is fundamentally a coarse- to very-coarse grained quartz-spodumene unit. The spodumene crystals, which are scattered irregularly through the much more abundant quartz, are 3/8 inch by 2 inches in average section and 8 inches in average length.

Gem-quality beryl, tourmaline, and quartz, the principal minerals mined, were taken mostly from one very large pocket that was encountered in the main workings. Quartz was particularly abundant and the output included one 148-pound crystal and several 40-pound crystals. Some of the quartz crystals were studded with partly intergrown tablets and thick prisms of beryl that ranged in color from white to salmon pink and rose pink. Many of these were as much as 1.5 inches in diameter. The principal pocket also contained many prisms of gem-quality tourmaline, some pink and some an unusual and beautiful blue-green. Several of these crystals are reported to have been at least six inches long and one-half to one inch in diameter. The core also contains lepidolite, muscovite, light-brown to reddish-brown zinnwaldite (rare), and cookeite.

The mine comprises two groups of workings, each in a relatively thick part of the main pegmatite dike. The southern group includes north, middle, and south cuts, which are irregular openings on a west-facing hill slope. The south cut, largest of the three, is about 25 feet by 40 feet in plan and 40 feet in maximum depth. An 18-foot drift extends northeast from its innermost face. The northern, or main group is on the opposite side of the ridge, and comprises three open cuts, a small, irregular stope, and about 200 feet of tunnels. The upper cut was developed downward as a stope when the principal mass of pocket pegmatite was encountered. Entry was later made at three progressively lower levels so that the stop ultimately was extended downward to a depth of at least 25 feet beneath the floor of the upper cut. The deeper part of the stope is an irregular room-like opening from which several short drifts project outward.

Although unusually fine gem material was taken from the Esmeralda deposit, the total production was rather small. Future production of gem-quality tourmaline and beryl plainly is dependent upon the discovery of other masses of pocket pegmatite, probably in the form of additional core segments. Exploration for such deposits might best be aimed at the down-plunge continuation of the main bulge in the dike. Although the coarse feldspar in the dike may be of potential commercial value, the amount is probably too small for future exploitation. The known amount of spodumene in the dike is trivial, and most of it has been so thoroughly altered that it now contains three percent or less of lithium oxide. Beryl is present in many different parts of the dike, but it is too sparse and too fine-grained in the outer units to warrant attempts at recovery. In the quartz-euhedral perthite pegmatite, where it is coarsest and most abundant, it forms less than 0.02 percent of the rock.

Footnotes:

1. This information is based on personal communication to F. H. Weber from R. H. Jahns in 1957. Need to check county records for mining claims to confirm dates and ownership.

2. According to Frederick J. Rynerson (1967), the mine was reportedly leased from a Mrs. Nickelson of Los Angeles to Tom Quin of San Diego, and himself. Rynerson, together with Doc Wilson of San Diego, briefly worked the deposit by developing a shallow cut across the vein. The date appears to have been sometime around 1904, but Rynerson places the date sometime between 1905 and 1914. Need to check county records for mining claims to confirm dates and ownership.

3. John Sinkankas made several notable tourmaline, beryl and quartz pocket discoveries during Martin's ownership, immediately adjacent to the old main workings. This activity was documented in notes, photographs, and mineral specimens in the personal collection of William F. Larson of Fallbrook, California.

Other Regions, Features and Areas containing this locality

References