Hooker Creek Mine, Lexington Hills, Santa Cruz Mts, Santa Clara Co., California, USA
|Latitude & Longitude (WGS84):||37° 10' 0'' North , 121° 57' 24'' West|
|Latitude & Longitude (decimal):||37.16694,-121.95667|
|Köppen climate type:||Csb : Warm-summer Mediterranean climate|
A Cu-Au-Ag occurrence/mine located in the center NW¼ sec. 10, T9S, R1W, MDM, 1.5 km (4,800 feet) E of Lexington Hills, and 7 miles S of Los Gatos, on the crest of the divide between Hendrys Creek on the N and Hooker Gulch on the S (above Aldercroft Heights development), on private land. Operated during the period 1917 to 1918. MRDS database stated accuracy for this location is 1,000 meters.
A highly mineralized zone in No. 2 adit is 85 feet (long ?). Local rocks include rocks of the Franciscan Complex, unit 1 (Coast Ranges).
Workings include underground openings with a length of 256.03 meters and comprised of 4 adits. The No. 1 adit is about 20 feet long; the No. 2 is about 235 feet; the No. 3 is about 85 feet and the No. 4 is about 500 feet in length.
Analytical data results: Ore from the No. 1 adit gave the following results: 18.13% Cu, 0.82 ounce Au and 0.60 ounce Ag/ton.
Commodity ListThis is a list of exploitable or exploited mineral commodities recorded at this locality.
4 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Paleocene - Late Cretaceous|
56 - 100.5 Ma
|Franciscan Complex, Melange|
Age: Phanerozoic (56 - 100.5 Ma)
Description: In New Almaden Block, in Franciscan central belt, melange with a matrix that consists of penetratively sheared argillite and lithic metasandstone, metamorphosed to pumpellyite- and, locally, lawsonite-bearing assemblages. Metasandstone of matrix locally exhibits a moderate cataclastic fabric (TZ-2A). Melange may contain blocks of high grade blueschist, amphibolite, chert, or mafic igneous rocks. Blocks of blueschist consist of glaucophane-, lawsonite-, and (or) jadeite-bearing schist, locally containing garnet. Amphibolite blocks consist of hornblende-bearing, foliated metamorphic rocks, largely of mafic composition, that also locally contain garnet. Hornblende in amphibolite blocks may be partially retrograded to sodic amphibole. Blueschist and amphibolite blocks commonly are sheared, subrounded to oblate, and may have external rinds composed of fine- to coarse-grained actinolite, talc, and antigorite, suggesting tectonic transport in serpentinite. Pre-metamorphic protoliths of blueschist blocks include eclogite, basalt, siliceous tuff, and tuffaceous metasedimentary rocks. Radiometric ages from elsewhere in Coast Ranges indicate Middle to Late Jurassic metamorphic ages (150-170 Ma) for these rocks. Blocks of chert are red, white or green, radiolarian-bearing, and locally tuffaceous. Chert may be locally foliated and contain blueschist metamorphic minerals, including lawsonite, sodic amphibole, jadeitic pyroxene, and stilpnomelane. Metavolcanic rocks of Bailey and Everhart (1964) that are not assigned to the Permanente or Marin Headlands terranes are shown as greenstone (gs) blocks in melange. In each of the structural blocks where melange occurs, its age is limited by the age of the youngest rocks incorporated in the melange. In most cases the resultant time of formation of the melange is younger than Middle to Late Cretaceous, and may extend into the early Tertiary. In Silver Creek Block and in Alum Rock Block, in Franciscan central belt, sheared black argillite, graywacke, and metagraywacke containing blocks and slabs of metagraywacke and shale (mw), chert and metachert (ch), serpentinite (sp), greenstone (gs), amphibolite, tuff, eclogite, quartz schist, greenschist, basalt, marble, conglomerate, and blueschist (bl). Blocks range in length from a few millimeters to several hundred meters. Only some of the largest blocks and slabs are distinguished on the map. In each of the blocks where melange occurs, its age is limited by the age of the youngest rocks incorporated in the melange. In most cases the resultant time of formation of the melange is younger than Middle to Late Cretaceous, and may extend into the early Tertiary. In Mt. Hamilton Block, in Franciscan eastern belt, melange with a matrix of sheared argillite, lithic metagraywacke, and scarce but diagnostic "green tuff" (Brandon, 1989). The matrix metagraywacke usually has a weak cleavage (TZ-2A) and contains fine-grained lawsonite, pumpellyite, and veins of quartz and aragonite. It is clear in some places that the metamorphic cleavage predates a scaly, anastomosing cleavage characterized by numerous slickensided surfaces that is typical of melanges everywhere (Raymond, 1973a). In most outcrops, however, the scaly cleavage is predominant and the more penetrative cleavage is no longer present. The melange occurs in two different modes that are evident on the geologic map. Thin melange zones occur within the coherent terranes (intra-wedge melange of Crawford, 1975), and thicker "inter-wedge" melanges separate the different terranes. Aside from the difference in scale, these two occurrences contain the same kinds of blocks and look the same in outcrop. The matrix contains abundant blocks and slabs of greenstone (gs) and radiolarian chert (ch) that are of the same metamorphic grade as the matrix and could be the dismembered basement to those sedimentary rocks. There are also blocks and slabs of metagraywacke (mw), conglomerate (cg), and graywacke (gw) that appear to have been incorporated into the melange from the adjacent, more coherent Burnt Hills and Yolla Bolly terranes by either sedimentary or tectonic processes. Some blocks of unknown type (?) have been mapped from topographic expression. Blocks smaller than about 100 m in diameter are not distinguished (except blueschist and other high-grade blocks shown by symbol).
Comments: New Almaden Block; Silver Creek Block; Alum Rock Block; Mt. Hamilton Block
Reference: Wentworth, C.M., M.C. Blake Jr., R.J. McLaughlin, R.W. Graymer. Preliminary Geologic Map of the San Jose 30 X 60 Minute Quadrangle, California. U.S. Geological Survey Open-File Report 98-795. 
|Cretaceous - Jurassic|
66 - 201.3 Ma
|Franciscan Complex, unit 1 (Coast Ranges)|
Age: Mesozoic (66 - 201.3 Ma)
Stratigraphic Name: Franciscan Complex; Dothan Formation; Honda Formation; San Luis Formation; Valentine Spring Formation
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052.