Old Hag prospect #1, Van Dam Peak, Poway, San Diego Co., California, USA

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Overview:

The foothills and mountain area around Van Dam Peak, north of Los Peñasquitos Canyon in the easternmost portion of incorporated Poway, just inside the original San Diego Corporate Boundary (SW/4 NW/4 SW/4 Sec 15, Township 13S, Range 2W, San Bernardino Meridian).

Geology:

A northeast trending series of pegmatite veins (late-Cretaceous 98-93 ma), measuring up to 10 feet thick, exposed along a strike distance of up to 1000 feet, and having a presumed steep to moderate southwest dip following the direction of plane of plutonic thrust and general degree of uplift and offset; The veins occur within gabbroic and granitic host rocks (mid-Cretaceous 105-120 ma). In between these veins are numerous stringers which form a randomly oriented pegmatitic stockwork. Indicative of higher temperatures, the pegmatites appear to be somewhat mica deficient, while orthoclase, quartz, and schorl are common as small interlocking crystals. The gabbroic country rock may contain minor Julian Schist components which caused localized devolatilization. In areas where these pegmatite veins and stringers intersect, graphic mineralization in which kaolin-filled pockets have been noted to occur. These hydrothermal pockets have produced many fine mineral specimens of microcline covered with epidote (possibly clinozoisite), and tourmalinated smoky quartz crystals up to 7 inches long and 4 inches in diameter. Much of the quartz discovered exhibits contact or penetration twinning.

History:

Discovered in 1990 by Michael Fender of Poway while hiking the numerous area trails and road cuts. The deposit was worked over 60 days within a two year period.

Workings and Production:

The workings are situated at an elevation of 1040' AMSL, approx 1000 feet NW of mountain top marked 1038' Van Dam Peak, being approx 150 feet west of the westernmost radio tower trail (road cut). The main development is a north trending trench 8' long by 4' wide x 4' deep created with hand tools while following the largest pocket discovered. Six smaller diggings followed on pockets nearby which each measured approximately 2 cubic feet.

The prospect is reported to have produced many large quartz crystal segments measuring up to 4 inches in diameter, and several perfectly formed single crystals up to 7 inches long and 2 inches across. Thousands of smoky quartz crystal points and floaters were produced, with hundreds of small tabular twinned crystals being recovered. One unique quartz intergrowth was reported to form a "perfect cross." Additionally, many clusters of quartz druse were found while digging. Nearly all of the quartz crystals were a light gray to deep orangey brown color, most being covered with tiny dark reddish black tourmaline needles and/or containing needles and hair-like inclusions (var: tourmalinated quartz). Microcline crystals were produced that had a "dusting" of micro epidote (possibly clinozoisite), and associations of quartz and schorl.

Notes:

The area is located on private lands, most of which is set aside as open space and habitat mitigation for lands disturbed by suburban development. The City of Poway informs visitors that all natural resources are fully protected. This includes plants, wildlife, and all natural features. Off-trail travel is prohibited. Please don’t shortcut trails or travel cross-country. All federal, state, and local regulations are in force.

Mineral List

'Clinozoisite-Epidote Series' Epidote

Kaolinite Microcline

Orthoclase Quartz var: Smoky Quartz

Schorl 'Tourmaline'

8 entries listed. 5 valid minerals.

References