The Colorado Quartz Mine, Mariposa County, California

 

Collector's Edge Minerals Inc. recognizes and thanks Rocks & Minerals for permission to use portions or all of their original article from "Rocks & Minerals", Volume 84, Number 5, pp. 396-412. Contributing authors were Bryan Lees, Collector's Edge Minerals, Inc.; Robert B. Cook, Department of Geology and Geography, Auburn University, Auburn Alabama; and Carl A. Francis, Harvard Mineralogical Museum, 24 Oxford Street, Cambridge, Massachusetts.  Collector's Edge has made some additions and changes to the original article which are incorporated below.

NTRODUCTION:

In January 1997, Bryan Lees, Collector’s Edge Minerals, Inc., became an investor in the Colorado Quartz Gold Corporation.
Through his mining expertise and specialized specimen collecting procedures and equipment, the "Dragon" was discovered, arguably the most famous world-class crystallized gold specimen ever found.  The "Dragon" has become the standard by which all crystallized gold specimens are measured!

LOCATION:

The Colorado Quartz mine is located in west-central Mariposa County, California, about 18 kilometers almost due north of the town of Mariposa.  It is along Colorado Quartz Road west of California Highway 140, northwest of the community of Midpines.  The mine, which is operated from the Mockingbird mine by the partial Artru patent, is in section 27, T. 4 S., R. 18 E., south of Saxon Creek.  It occupies an approximately 11-acre patented claim and several adjoining unpatented claims.  It is near the old mining camp of Colorado (Castello 1921) and may be assigned to either the Colorado or the Whitlock district (Clark 1970).  The Colorado Quartz and surrounding mines are privately owned and not open to collecting.

There are two distinct sets of mine workings on the property, and this has led to some confusion about names.  The original workings along the Colorado vein are traditionally considered the Colorado mine.  The present workings along the parallel Colorado dike are best described as the Colorado Quartz mine, allowing for a modern distinction between the two mines.  This is particularly important given that the two mines are not connected on this property and the dike system along which the present mine is being developed was not worked until the 1970s.  Historically, there have been three types of mining claims permitted.  These are placer, lode (in this case vein-type), and mill site.  It has been common practice to insert the word quartz into a claim’s name to designate it as a quartz vein-type lode claim rather than a placer or mill site, particularly if the latter two also exist in the district.  It is not known when the word quartz was first formally applied to the workings on the present three claims, but we suspect that it predates the discovery of the pocket gold occurrences along the Colorado dike and may well have been applied to the older working along the Colorado vein.

Map of Colorado Quartz mine surface and partial underground workings.  Inset:  General location map of the mine.  Prepared by William Besse.

Colorado Quartz mine head frame.  Carl Francis photo.

HISTORY:

The history of the original Colorado and present Colorado Quartz mines through 1981 was given in detail by Kampf and Keller (1982), from whose work much of the following information covering that period has been abstracted.  Various regions in California were mined for gold by Sonoran Mexicans prior to the 1840s.  Following the great California gold rush, the town of Mariposa became a mining center and boom town.  During this era, the local miners followed alluvial gold occurrences back to their respective lode sources, occasionally making successful hard-rock discoveries.  Today, the old workings of these gold miners can be found in the Mariposa area, including in the immediate vicinity of the Colorado Quartz mine.  Early in the history of the Colorado district, the larger mines were along the Colorado vein; however, it ultimately became apparent that the most prolific specimen claims – today known as the Colorado Quartz mine – followed a parallel feature, the Colorado dike.  Of the properties along the Colorado dike, the Colorado Quartz and the Mockingbird share the distinction of producing some of the finest crystallized gold specimens ever found.

An attractive 6.8 x 4.0 x 2.7-cm aggregate of crystalline gold and quartz.

Published records indicate that placers along Saxon Creek in the Colorado district were known to be quite rich as early as 1852 (Allsop 1853) and that by 1855 the district was very active, boasting a post office from 2 June 1858 to 26 March 1860 (Gudde 1975).  However, no mention of the Colorado Quartz mine appears until 1 February 1875, when a patent application for a 1,250x400-foot parcel of land in what was then called the Mariposa Quartz mining district was filed by John A. Bataille, a merchant in the town of Colorado.  The object of Bataille’s efforts appears to have been the Colorado vein rather than the specimen-productive Colorado dike.  Bataille sold the mine in 1885 to P.W. Judkins, C.H. Weston, and I.L. Dearborn of Mariposa.  The property remained in the hands of these three families until 1974, when it was sold to David A. Grimes Sr.

The history of the mine is poorly known for much of the first decades of the twentieth century.  A ten-stamp mill was constructed on one of the unpatented claims in 1912 or 1913 to treat ore from the Colorado vein.  By 1914 the workings included a 200-foot inclined shaft, a 500-foot-long adit level, a 119-foot ventilation raise, and a second 75-foot raise.  Surface facilities included an assay office, change house, bunkhouse, office, and storeroom (Lowell 1916).  Remains of this old mill are still evident today, as are some of the associated workings, all of which appear to have been on the Colorado vein rather than the Colorado dike; this part of the workings was referred to in subsequent reports as the Colorado mine.

The mine was temporarily closed in 1918 and remained generally inactive until November 1927, when it was leased to a syndicate called the consolidated Gold Fields of Mariposa, Inc.  This syndicate reported production valued at $50,000 between 1927 and 1936.  The syndicate lost its lease on the Colorado mine in 1936, and development was resumed by Perry Judkins Jr. and John Vowel, heirs of the earlier owners.  The mill was expanded, and two ore shoots on the 190-foot level were developed.  The mine closed in 1937 as a result of an unfortunate accident that happened to Judkins.  World War II prevented further development, and by the end of the war the shaft had caved.  By 1953 most of the buildings were gone, and no equipment was left on the property (Bowen and Gray 1957).

The modern era of activity at the Colorado Quartz mine began in February 1974 when David A. Grimes Sr. purchased the mine and formed the Mariposa Mining Company.  Later in the year, Grimes began sinking a new shaft in a gully some 1,500 feet from the original Colorado mine in the hope of intersecting the old workings.  Instead, he encountered the Artru workings along the Colorado dike, a zone long known in the Mockingbird mine for crystallized gold.  Extending these workings rather than drifting over to the Colorado vein, Grimes found his first pocket late in 1974, reportedly selling its contents for bullion value.  Grimes sold the mine to Unlimited Minerals of Detroit, Michigan, in March 1975.  This group began sinking a larger shaft on the ridge just west of Grimes’s original shaft but soon abandoned this work due to insufficient capital.  They then returned to Grimes’s workings and soon discovered large amounts of crystallized gold.  One account indicates that approximately 350 ounces of gold were found during the summer of 1976.  An unknown quantity of this gold was apparently high-graded by the miners and sold on the European market, with the remainder being sold by the company at slightly more than its bullion value.  Good descriptions of some of the best gold from this find are given by Eidhal (1977), and a description of the intrigue associated with the sale of this gold during the late 1970s is provided by Leicht (2008).  Grimes was not paid the agreed-upon royalty (in gold) and by October 1977 had regained legal title to the mine.  He immediately renewed mining and quickly found a significant pocket of crystallized gold.  Soon thereafter, heavy rains and resulting pumping issues forced closure of these workings.  Grimes then returned to the new shaft begun by Unlimited Minerals.  He deepened the shaft to 86 feet, at which point he began drifting along the dike-slate contact.  Grimes found more pockets, and by spring 1979, he had driven approximately 300 feet of drift.  Grimes sold the mine in June 1979 to Colorado Gold, Inc. of Fallbrook, California (Buzz Gray and Bill Forrest of benitoite fame), who, although finding some fine gold specimens (Bancroft 1987), suspended operations in 1987, offering the property for sale at that time (Leicht 1987).

Because of this history of producing what were up to that time arguably the world’s finest crystallized gold specimens, the mine was purchased and reopened in late 1988 by the newly formed Colorado Quartz Gold Corporation, with Larry Lehto as president.  Between1989 and 1994, the mine was worked intermittently, depending upon available funds, mine permit issues, and personnel availability.  The mining effort concentrated on rehabilitating the original shaft and opening up the old 80-foot level.  After 1994, the mine went on full-time work status and operated almost continuously through 2001.

In 1994, the company added new investors, John and Lucretia Emmett of Clovis, California (current owners of the Mockingbird mine.).  Infused with new cash and equipment, the company increased its exploration efforts.  During 1994, a surface trench was excavated, and several pockets were recovered.  The proceeds were used to pay off old mine debts and make the operation solvent.  The value of the material from the July 1994 find is estimated at about $1 million in 2009 dollars.

Between July 1994 and December 1995, a shaft was sunk from the 80-foot level to the 140-foot level.  Immediately upon reaching the 140-foot level in early 1996, another pocket zone was hit.  It produced the famous “Pocket Piece” containing approximately 40 ounces of crystallized gold.  The details of this specimen’s delicate extraction and preparation and a complete description of it have been given by Wilson (1996).  In now resides in the Houston Museum of Natural Science.

On 21 January 1997, the Colorado Quartz Gold Corporation added a new investor in the mining effort.  The new investor was Colorado Quartz Gold, LLC. which was made up of four people:  Jim Duncan of Indianapolis, Indiana; Bryan Lees of Golden, Colorado; John Lucking of Phoenix, Arizona; and Gene Meieran of Phoenix, Arizona.  Again supplied with new cash, the corporation continued drifting at the 140-foot level southeastward toward the property boundary; after a year a pocket zone was hit in January 1998.  This new zone produced the “Dragon” specimen, which was found in the wall of a raise using a metal detector just after a blast.  The specimen was extracted by Larry Lehto, Noble Sparks, John Emmett, and Bryan Lees in a block of matrix using a diamond-bladed chainsaw, and it was subsequently prepared in the lab of Collector’s Edge Minerals.  After passing through several hands, the "Dragon" is now in the Houston Museum of Natural Science where it resides alongside its sibling, the Pocket Piece.  The "Dragon" is perhaps the most famous modern crystallized gold specimen, and the estimated 7 ounces of contained gold is probably the most valuable by weight ever found.

John Emmett, owner of the adjacent Mockingbird mine, using a metal detector which helped locate the "Dragon” prior to its removal.

The "Dragon" specimen in place with minor matrix removed to partially expose some of the gold.

John Emmett using a diamond-bladed chain saw to cut slots around the "Dragon” to
facilitate its removal.

Miners in the Colorado Quartz mine office looking at the "Dragon” prior to stabilization and shipment to Collector’s Edge Minerals for cleaning and preparation.

By June 1999, the 140-foot level was developed to the property boundary with few additional showings of gold.  Beginning on 28 June 1999, development work was initiated to reach the 180-foot level.  This required sinking the shaft an additional 40 feet, which was completed in early 2000.  At that point, the 180-level drift was started along the vein parallel, but 40 feet beneath the 140-foot level to ultimately access the area 40 feet beneath the Dragon gold specimen discovery site.  It was hoped that there were additional treasures waiting to be found.  After completion of the drift, a stope was developed all the way up to the Dragon gold area.  Unfortunately, all this activity produced only one small gold specimen.

In 2001, with the onset of unfavorable economic conditions in the aftermath of 9/11, Colorado Quartz Gold Corporation decided to suspend operations and either look for new investors or explore the possible sale of the mine.  The property sat idle until mid-2006 when the mine was sold to Colorado miner/investor Lance Barker.  Barker, his son Max, and fellow miner Matt Ingram are extending workings on the 140-foot level and carefully developing stopes along both the east and west dike contact.  In the process they have discovered two world-class gold specimens (named “El Fuego” and the “Bristlecone”) and a number of small, though still outstanding pieces (Moore 2009).

GEOLOGY:

The Colorado Quartz mine lies immediately east of the southern part of California’s famous Mother Lode system in a subsidiary district (Ransome 1900; Knopf 1929).  The Mother Lode proper extends down a north-south trend along the west flank of the Sierra Nevada for more than 150 kilometers, from near Georgetown in El Dorado County on the north to a few kilometers south of Mariposa, in Mariposa County.  Its persistent quartz lodes are generally related to the Melones Fault zone or system whose trace is commonly marked by bold outcrops of north-trending milky quartz veins.  In Mariposa County, the Mother Lode is bounded on the east and west by parallel flanking groups of interrelated gold-quartz veins that collectively form the “east” and “west” gold belts.  The Colorado Quartz mine is near the western edge of the east gold belt; like many of the other crystallized gold specimen-producing mines for which California is famous, it does not lie within the Mother Lode itself.  Mariposa County geology has been described in varying detail in Bowen and Gray (1957), Lowell (1916), and Preston (1890), to which the reader is referred for additional details.

Geologically, the Colorado Quartz mine is strikingly similar to the nearby Mockingbird mine (Cook and Gressman 2008).  Two dominant though different lithologies host and/or control the location of gold-bearing quartz veins currently exploited at both mines.  The productive and gold pocket-bearing parts of quartz veins occur at or very near the contact of a northwest-trending, intensely altered mafic dike, the Colorado dike, that extends apparently uninterrupted from the Colorado Quartz mine claims across the Artru property and on through the entire length of the Mockingbird claim.  The dike is hosted by a silty graphitic slate known locally as the Briceburg Formation.  The Briceburg Formation appears to be equivalent to the Mariposa Formation of Ransome (1900) and is likely of late Jurassic age (about 140 million years ago); it contains minor interbedded sandstone and conglomerate.

The Colorado dike varies locally in thickness and attitude but in the immediate mine it dips steeply northeast and strikes approximately N.50o W.  In the Colorado Quartz mine it exhibits a more uniform thickness than in the Mockingbird, where it varies in thickness from 3 to 7 meters.  Compositionally, the dike has been described by Kampf and Keller (1982) as greenstone, a mafic rock that has been “propylitically altered.”  In this type of alteration, mafic minerals and calcic plagioclase are hydrothermally altered to produce a rather uniform rock containing serpentine and chlorite minerals, calcite, epidote, and iron sulfides and/or oxides.  Both the brittle, altered dike and the immediately adjacent slates have undergone mineralization during a weak post-Jurassic folding event.  At the surface, the dike is deeply weathered and is accompanied locally by narrower, though similar, variably altered, barren dikes of apparently the same generation.  Its contact with the slate host is locally quite sheared and marked by swarms of subparallel, generally barren quartz stringers.  Locally, quartz veins within the dike itself show apparent drag folding, suggestive of progressive down-dropping of the dike to the northeast in the immediate Colorado Quartz mine are.

About 100 meters southwest of, and parallel with, the Colorado dike is a zone of discontinuous banded quartz veins known as the Colorado vein.  Although historically described as an essentially continuous vein, exploration trenching indicates that this typically narrow zone of discontinuous quartz veins actually marks the margin of an altered dike, generally similar to the Colorado dike.  At many places, its position is marked primarily by the dike and almost insignificant contact silicification.  Elsewhere, as in the vicinity of the old Colorado mine workings, the quartz is vein-like and approaches 5 meters in width.  The Colorado vein is not known for crystalline gold but has been the source of moderate-grade gold ore on the Colorado mine property that is sufficient for mill feed.  The Colorado vein strikes to the northwest and dips to the northeast somewhat less steeply than the parallel Colorado dike.

The productive quartz veins in the Colorado Quartz mine have been referred to as floor veins, a carryover from similar veins in other pocket mines where miners commonly use the shallowly dipping veins as the floor for stopes; an example of this technique was described by Leicht and Cook (2004) for the Eagle’s Nest mine in Placer County.  At the Colorado Quartz mine, floor veins typically consist of locally vuggy, milky white quartz, and very from about 2 cm to as much as 25 cm thick.  They are almost everywhere barren of gold or sulfide minerals.  Floor veins are best seen where they cut the dike proper.  When viewed in a vertical plane perpendicular to the strike of the dike (looking into the dike in an up-strike or down-strike direction), floor veins appear to lie more or less horizontally across the dike, making a right angle with the dike walls except where minor drag folds have deflected them commonly upward.  When viewed from the side (looking at the edge of the dike where its plane of contact with the adjacent slate has been exposed during mining), they are seen to dip gently to moderately (up to 50 degrees) to the northwest.  Floor veins do not typically end at the dike-slate contact but commonly extend into the slate for as much as several meters.  The most productive parts of these veins in mines along the Colorado dike have traditionally been at the dike-slate contacts, although major specimens in the Colorado Quartz mine have been found up to 0.4 meters into the dike as well as short distances into the slate.  The intense search for gold-bearing pockets in mines along the Colorado dike has resulted in the identification of poorly understood structures called cutters by the miners.  Cutters in the Colorado Quartz mine are seen as near-vertical, variably quartz-filled, joint-like fractures that strike across the dike at shallow angles, gently intersecting dike-slate contacts, and extending into the adjacent slate.  The most productive areas are thought to be where cutters intersect floor veins at or very near the dike-slate contact, although the most recent successes do not appear to be related to cutters.

An unknown number of gold-bearing pockets and many more vuggy but barren pockets in floor veins have been found since the period of modern mining began in 1974.  Most productive pockets have been small zones in otherwise massive quartz floor veins that contain crystalline gold in amounts sufficient for one or more specimens; others contain masses of variably crystallized gold weighing up to 40 ounces and tightly contained in surprisingly small clay-filled and iron and manganese oxide-filled pockets.  Spectacular pockets have been found on both sides of the dike at the Colorado Quartz mine, whereas the spectacular discoveries of 2006 in the Mockingbird mine were only along the south-west dike margin.  Surface development of the dike-slate contact by John Emmett in 1994 on the Colorado Quartz property resulted in the discovery of several significant weathered pockets.  Pockets are generally irregular in shape and small (up to about 20 cm), although barren vugs up to about 1 meter in maximum dimension have been found along the dike.

Gold:  Au

Gold occurs locally in massive form in the milky quartz floor veins, but not in sufficient quantity to be a reliable ore or of significant value to be mined as specimens.  Consequently, the mine is operated exclusively for crystallized gold specimens that are recovered from vugs.  The study by Kampf and Keller (1982) revealed unusual morphological complexity for Colorado Quartz mine gold, as illustrated by a variety of specimens including a 0.1-mm-diameter crystal (on a larger mass of crystallized gold) showing the cube a{100}, octahedron 0{111}, hexoctahedral {124} and x{1.10.18}, and also a tiny octahedron modified only by the x form.  Cook  and Gressmean (2008) describe a 1-cm dodecahedron isolated on quartz from the adjacent Mockingbird mine.  These crystals, which look like figures in a textbook, are exceptions, and only rarely do the crystals show ideal forms (cf. Francis 2004).  Typical specimens are groups of irregular arborescent or dendritic crystals that show flattened octahedrons at their edges.

Examination of larger Colorado Quartz mine specimens shows that gold nucleates in quartz at the edge of a cavity and grows into it, branching in two or three dimensions as space allows.  The branches may be fragile and fall apart, perhaps accounting for the large number of small, loose crystal groups reported.  Observations made during the preparation of the Pocket specimen illustrate this feature.  Gold, while in solution, migrated through cracks and into openings such as the Pocket void.  Because the cracks are extremely small, as gold enters a void it begins crystallizing as very fine threads, wires, and/or ribbons.  As the gold continues to crystallize, it grows within the cavity, at times resulting in berry-like crystal aggregates that belie the underlying delicate matrix connection.  With its weak attachment and its high specific gravity, almost any individual gold crystal is in danger of falling off the cavity wall.  Often pockets are encountered in which the gold crystals are lying loose in the pocket’s bottom.  In the case of the Pocket specimen, several gold leaves and crystals were discovered lying loose within the cavity.  However, many were protected by the subsequent crystallization of the pocket-filled clay that preserved the extremely delicate gold leaves, protecting them from coming off the pocket walls.

Because of their beauty and rarity, many of the finest Colorado Quartz mine specimens are illustrated in the literature, and much can be learned from their examination.  Early photographs(e.g., Eidahl 1977) show small specimens composed of plates of skeletal octahedra occasionally associated with quartz.  A miniature with four crystals “marching” along the edge of a small piece of matrix is particularly memorable (Thomssen 1996), but groups and plates of parallel octahedra are more typical.  At least eight large (more than 10-cm) Colorado Quartz mine gold specimens are now on record, and these clearly illustrate how variable the habit may be in a single vug, even on a single specimen.  A 10-cm two-dimensional specimen illustrated by Kampf and Keller (1982) shows rounded and elongated, poorly formed crystals on branches at the top of the specimen but thick, lustrous sheets at the bottom.

Two of the most remarkable Colorado Quartz mine specimens are the Pocket Piece and the "Dragon".  Wilson (1996) described and illustrated the Pocket specimen, which represents an entire vug 26 cm across.  The "Dragon" comprises a 12-cm-tall crystal plume rising from an approximately 10x10-cm matrix of quartz and slate.  The prominent upper part is a two-dimensional crystal.  Flattened crystals at the tips of the branches have triangular or hexagonal shapes with raised edges.  Three-dimensional but skeletal octahedra, to 2 cm on edge, form the body of the "Dragon" and the two “legs” in the middle of the matrix!

Numerous other specimens were produced during the Lehto period of ownership, but because they have been over-shadowed by the Dragon, they are not nearly as well known.  One that especially deserves mention because it is so unlike any other Colorado Quartz mine specimen is a chunky, 3-cm V-shaped pair of crystals whose individual shapes appear unrelated to ideal cubic crystal forms.

The new mine owner, Lance Barker, discovered several pockets in early 2008.  "El Fuego" and "Bristlecone" are the names given to the largest and best of the thirty-two new miniature to cabinet-sized specimens mined by Barker and offered by Collector’s Edge Minerals, Inc. at the September 2008 Denver Show (Moore 2009).  "El Fuego" consists of two 5-cm crystallized leaves rising from a white quartz matrix that is 12 cm wide.  One leaf is composed of equant crystals, the other has more elongated crystals at its edges.  In contrast, the 12-cm "Bristlecone" specimen is a compact mass of rounded crystals on branches growing out and to the right.

The smaller pieces show a remarkable range in character, typical of the mine’s entire production.

“El Fuego”, specimen is 12.6 cm across.

The “Bristlecone” prior to cleaning and preparation.

The “Bristlecone” after final cleaning and preparation.

SPECIMEN PREPARATION

The unusual beauty of most gold specimens seen at gem and minerals shows or in museums is far different from their original appearance, and the preparation of good specimens has become an art requiring significant expenditures of both time and money.  Colorado Quartz mine specimens are no exception.  For example, when finally removed from the mine, the Pocket Piece specimen resembled a cracked green and white block, about 14 inches square with some loose fragments.  The specimen was so fragile that it had to be held together with metal bands and epoxy.  The piece was transported to Collector’s Edge Minerals, Inc. in Golden, Colorado, where the matrix was stabilized using high-strength two-part epoxy.  During the next several months, the specimen was carefully studied, cleaned, and prepared by Collector’s Edge “rock doctor” Robert Lorda.

Robert Lorda next to the “Pocket Piece”.

The “Pocket Piece” - note the bracing used to secure the specimen for shipping.

Several challenges presented themselves early on in the cleaning process., foremost of which was the tough coating of chloritic clay that filled the entire pocket cavity encasing the gold, quartz, and other matrix constituents within the specimen.  This had to be removed without damaging the lustrous gold underneath.  Lorda accomplished this by using bamboo sticks and a special ultrasonic dental tool.  The clay was so tenacious that only 1 mm could be flaked off at a time.  It was very important to remove the clay in such a manner so as to not weaken the support for the delicate crystalline gold leaves.

To understand where the best gold was located within the block, two techniques were incorporated:  First, the specimen was shown to a local veterinarian who had an X-ray machine.  Images were taken showing exactly where the best, thickets gold sections were located.  Following X-ray imaging, the specimen was electrically “mapped” using a volt meter.  The mapping process allowed the preparatory to understand how the gold was interconnected prior to removal of the clay.

Together with imaging and mapping, the cleaning process proceeded to the point where all of the gold leaves were exposed.  Many of the gold crystals and leaves showed a tendency to be very delicately connected to the matrix.  As the gold leaves were being exposed, their “roots” could be followed downward into the matrix where they were barely attached.  Clay removal was halted before the leaves became unstable and in danger of coming off the pocket wall.

The cleaning of the Pocket Piece took almost six months, but the mine owners were rewarded with one of the finest gold specimens ever discovered and probably the first entire pocket of crystalline gold ever preserved for future scientific study.  It is estimated that more than 40 ounces of gold are contained in the specimen.

The finished “Pocket Piece”

Like the "Pocket Piece" specimen, the matrix of the "Dragon" was very fragile and had to be reinforced with wire and glue before being taken to Golden where it was prepared.  Having had the previous experience with the Pocket Piece, there was a well-established procedure for stabilizing and preparing this new specimen.  This time Bill Hawes was handed the task.

Bryan Lees, CEMI, with the "Dragon” before cleaning and preparation.

Closer view of the "Dragon” as it was received at Collectors Edge.

The "Dragon” during preparation.  Notice at the bottom the “legs” beginning
to show and the “head” beginning to show at the top.

Care was taken to first clean and expose the gold.  When it was fully exposed, the gold took on an interesting shape, and it was decided to remove the matrix from around the “top” of the piece.  The matrix was cut away using diamond tile-cutting saws; the cuts were obscured by sculpting the rock with small, pneumatic carbide-tipped tools.  The specimen was almost completely prepared when it was discovered that there was additional gold to be exposed along the “bottom” of the specimen.  The gold in this area was concealed within a druse of quartz.  After two more days of work, the gold at the specimen’s base was exposed revealing the “legs” of the piece.  Its shape, especially with the removal of the gold along the base, was instantly recognizable as a “Golden Dragon”.  Although containing only approximately 7 ounces of gold and in no way resembling its original appearance, this specimen certainly ranks as one of the finest crystallized gold specimens in the world.

The "Dragon” after preparation.

This 8.1 cm-high gold and quartz specimen is one of the finest yet found in the
Colorado Quartz mine.

A large 14.6 x 7.6 x 1.7-cm, crystalline gold mass on quartz.

An aesthetic 5.7 x 5.0 x 3.1-cm gold on quartz specimen.

A heavy 6.0 x 3.7 x 1.5-cm mass of crystalline gold and minor quartz matrix.

A small miniature of complexly crystallized gold on quartz, 2.5 x 2.6 x 1.4-cm.

A 4.2 x 3.5 x 3.0-cm specimen consisting of crystallized sheet of gold on quartz.

A well-crystallized 2.7-cm high gold specimen.

An unusual thumbnail-sized mass of crystallized gold.

A 4.5 x 2.5 x 1.3-cm crystallized gold on quartz specimen.

An unusual group of flattened gold crystals with minor slate matrix.

A fine 6.9-cm high group of octahedral gold crystals.

A 3.4 x 2.3 x 1.7-cm crystallized mass of gold.

An attractive 3.0 x 2.1 x 1.8-cm irregular mass of gold and minor quartz matrix.

A fine 10.4 cm high matrix gold specimen.

An aesthetic 3.0 x 3.2 x 1.9-cm specimen consisting of a sheet of crystalline gold on quartz.

A 3.1 x 1.7 x 1.1-cm mass of crystallized gold on white quartz.

A magnificent 6.5-cm group of gold crystals.

An unusual 2.9-cm divergent group of gold crystals.

A 12.6 cm high specimen of gold on matrix.

A 2.4 cm hoppered octahedral gold crystal specimen.

An unusual gold on quartz specimen.

A very esthetic hoppered gold specimen.

A crystalline gold specimen extending from a pocket lined with quartz crystals.  Approximate specimen size is 8.5 cm x 10 cm.

OTHER MINERALS:


Ankerite:   Ca(Fe,Mg,Mn)(CO3)2

Ankerite occurs as grayish cleavable masses of ankerite associated with some vuggy floor veins, rarely associated with crystalline gold.

Arsenopyrite:  FeAsS

Arsenopyrite is occasionally associated with pockets, particularly in areas where they are gold-bearing.  In general, the arsenopyrite occurs in small crystals or is coarse-grained but massive.  Although weathering is relatively deep, no secondary arsenic minerals produced by the supergene processes acting on arsenopyrite have been observed.

Calcite:  CaCO3

Calcite occurs in good crystals to 2 cm across with quartz crystals in floor vein vugs.  The crystals are often colorless and transparent, although attractive creamy tan to yellow crystals on limpid quartz were seen at the Mockingbird mine.

Galena:  PbS

Galena occurs as nondescript small masses in floor veins near pockets.  It is rare and is unknown in collectible specimens.  Its presence is thought to signal the occurrence of gold-bearing pockets and thus is a reason for optimism.

Pyrite:  FeS2

Pyrite occurs sporadically in host and dike rock near quartz veins and locally in fine-grained nodular masses in the Briceburg Formation.  What are thought to be pyritized fossil shells have been found by the miners in the Mockingbird mine.  Collectible pyrite specimens are unknown from the Colorado Quartz mine, although microcrystalline phrite has been found coating gold on some specimens.

Pyrrhotite:  Fe1-xS

Pyrrhotite has been reported by the miners at the Mockingbird mine and is assumed  to occur in the Colorado Quartz ores.  Where observed in the Mockingbird, pyrrhotite occurred as massive, narrow strings associated with the margins of some floor veins.  It was first noted because of its interference with metal detectors, giving false positive signals in discrimination mode.

Quartz:  SiO2

Quartz is the dominant vein mineral.  Vugs are common in floor veins near the contact between the Colorado dike and the enclosing slates.  According to Bancroft (1987), miners in the Mockingbird mine had recovered in the 1980s about 360 kilograms of quartz crystals, presumably from a single pocket or pocket zone.  Individual crystals are up to 4 cm across and groups are up to 25 cm.  Many crystals contain chlorite inclusions and phantoms.  Eidahl (1977), in describing the discovery of the major April 1976 gold pocket, also describes a large quartz crystal pocket found on the old 40-foot level.  About “200 pounds of hand-size and larger quartz crystals and groups” were removed from the pocket.  The crystals were water-clear throughout except for milky bases.  Minute gold crystals occurred along fractures in the quartz.  Limpid, mirror-faced quartz crystals to 2 cm long in plates to 12 cm across were seen at the Colorado Quartz mine in February 2009.

CURRENT STATUS:

The workings of the modern Colorado Quartz mine do not reflect a history of early historical mining, although caved adits and shafts and the old mill facility that serviced parallel working on the Colorado vein up-strike from the current mine are certainly in evidence The accessible modern workings on the Colorado dike do not resemble the old, somewhat chaotic upper levels of the nearby Mockingbird mine.  They have been orderly and methodically developed.  The surface facility consists of an electric hoist and head frame, a mill building that no longer contains any useful equipment, an office-residence-shop building, and a trailer pad.  The mine has three significant levels at 80, 140, and 180 feet below surface, referred to as the 1,2, and 3 levels, respectively.  The initial work that resulted in discovery of the spectacular April 1976 pocket, was done by drifting a few tens of meters at a depth of only 40 feet (Eidahl 1977).  Current mining utilizes compressed air-driven stoppers and jacklegs; development drift rock is loaded with an Eimco mucker.  Haulage is with a 1-ton rail car, with as many as eighty carloads of rock trammed by hand and hoisted in a single shift.

Access to the mine is by the concrete-lined vertical shaft adjacent to the shop and residence building.  Considerable work was done on the 80-foot level on both sides of thed dike, generally to the southeast toward the common Colorado Quartz-Artru boundary.  Much of this level is dangerous and currently inaccessible.  Today, the 140-foot level is active and has been the site of the recent major discoveries.  Drifts follow both sides of the slate-dike contact for approximately 400 feet southeast of the shaft.  Drifting is continuous on the southwest side of the dike and discontinuous, with a cumulative length of 200 feet, on the northeast side.  Access to the northeast slate-dike contact drifts is by regularly spaced crosscuts through the dike from the continuous drift along the southwest side of the dike.  Drifting on the southwest side of the dike also extends for 100 feet northwest of the shaft on the 140-foot level.  Both the Bristlecone and the Dragon specimens were discovered by stoping and/or ramping upward from the 140-foot level on the northeast dike-slate contact at a point some 250 feet southeast of the shaft.  Interestingly, El Fuego was found about the same distance southeast of the shaft as the Dragon but along the southwest slate-dike contact about 10 feet above the 140-foot level.  The 180-foot level is currently flooded and is used as a sump.  Workings here consist of about 480 feet of drift along the dike-slate contacts, mostly southeast from the shaft.  A stope-like incline was driven upward fro this level along what is now referred to as the Dragon zone.

Unlike past efforts that focused on developing discreet, hopefully productive structures or floor veins, the current mining method is by a series of methodically developed shrinkage stopes along the slate-dike contact upward from the 140-foot level toward the 80-oot level.  In this mining method, all rock within a 6-8 foot-wide slice at the slate-dike contact is mined, eliminating the chance of missing the next world-class specimen.  Access to the active slot-like stopes is by raises that extend to the top of the broken rock surface near the top of the shrink stope.  After each blast, enough rock is pulled from regularly spaced chutes along the 140-foot level to draw down the broken rock surface at the top of the stope, use of diamond-bladed chainsaws, employing a technique pioneered at the Sweet Home mine to remove rhodochrosite in the 1990s (Bartos 2007).  In this technique, the entire pocket is cut out by the diamond-bladed chainsaw, often resulting in large green-and-white pocket-bearing blocks of quartz and dike or slate matrix.  These blocks are typically fractured and too fragile to transport and must be held together with metal bands and epoxy for shipment to the preparation lab.  Broken waste rock drawn from the chutes at the bottom of the stopes is trammed manually to the shaft and raised to the surface for disposal.

REFERENCES:

Collector's Edge Minerals Inc. recognizes and thanks Rocks & Minerals for permission to use portions or all of their original article from "Rocks & Minerals", Volume 84, Number 5, pp. 396-412.  Contributing authors were Bryan Lees, Collector’s Edge Minerals, Inc.; Robert B. Cook, Department of Geology and Geography, Auburn University, Auburn Alabama; and Carl A. Francis, Harvard Mineralogical Museum, 24 Oxford Street, Cambridge, Massachusetts.

Allsop, T. (1853) California and its gold mines. London.

Bancroft, P. (1987) Mockingbird mine to reopen.  Mineralogical Record 18:92-96.

Bartos, P.J. (2007)  Specimen mining at the Sweet Home mine in Colorado’s Alma district, Mining Engineering 59:8, 29-35.

Bowen, Jr., O.E., and C.H. Gray Jr. (1957)  Mariposa County lode mines.  California Journal of Mines and Geology 53 (2); 69-187.

Castello, W.O. (1921)  Colorado district.  California Bureau of Mines report 17.

Clark, W.B. (1970)  Gold districts of California. California Division of Mines and Geology bulletin 193.

Cook, R.B., and T.M. Gressman (2008)  The Mockingbird gold mine, Mariposa County, California.  Rocks & Minerals 83:392-401.

Eidahl, D. (1977)  Gold from the Colorado Quartz mine – California’s newest source of fine specimen gold.  Mineralogical Record 8:440-41.

Francis, C.A. (2004)  Gold crystals – A primer.  Rocks & Minerals 79:24-29.

Gudde, E.G. (1975)  California gold camps.  Berkeley: University of California Press.

Kampf, A.R., and P.C. Keller (1982)  The Colorado Quartz mine, Mariposa County, California:  A modern source of crystallized gold.  Mineralogical Record 13:347-54.

Knopf, A. (1929)  The Mother Lode system of California. U.S. Geological Survey professional paper 157.

Leicht, W. C. (1987)  The history of crystallized gold  in California. Mineralogical Record 18:33-40.

--(2008) California Gold –Nevada, Mariposa, and Placer counties.  In American mineral treasures, ed. G.A. Staebler and W.E. Wilson, 20-27, East Hampton, CT: Lithographie.

Leicht, W.C. and R.B. Cook (2004) The Eagle’s Nest mine, Placer County, California, Mineralogical Record 35:65-72.

Lowell, F.L. (1916) Mariposa County.  California Bureau of Mines report 14.

Moore, T.P. (2009) What’s new in minerals – Denver Show 2008, Mineralogical Record 40:71.

Preston, E.B. (1890) Mariposa County.  In Geology of the Mother Lode region, 300-310.  California Bureau of Mines report 10.

Ransome, F.L. (1900) The Mother Lode district folio, U.S. Geological Survey geological atlas of the United States, folio 63.

Thomssen, R. (1996)  Gold.  In The F. John Barlow mineral collection ed. F.J. Barlow, R.W. Jones, and G.L. LaBerge, 173-203.  Appleton, WI: Sanco Publishing.

Wilson, W.E. (1996)  A world-class gold from the Colorado Quartz mine, Mineralogical Record 27:429-32.