Sinkankas Notebook

The following notes, by John Sinkankas, were a memorialization of his visit to the Esmeralda Mine, on the weekend of September 22–23, 1956. An earlier visit, on Sunday, March 11, 1956, also is recounted. These come from the collection of Pala International’s president Bill Larson.

Mack [Oliver Perry McMican], myself, Johnnie, and Jim Gray went up to mine this weekend. Work was continued on the northeast end of the blowout on the main dike at the point where the ledge is thickest. Sections of ledge were removed from the top and rolled down the hill. The streaks of pocket mineralization which had yielded pockets of blue tourmaline were again apparent here. Dike units showed the usual friable albite mineralization, green muscovite, large black tourmalines, blackish manganese oxides, etc.; also garnet, much stained. Just inside is the gem bearing unit of coarse blocky perthite/granular quartz. A total of three pockets were found, one being substantial and yielding most of the material recovered.

The association of cracks in the dike to mineralization and pocketing was again brought out clearly here although the largest pocket was not split vertically by cracks, being enclosed completely in perthite on the bottom. However, its upper part was broken through by horizontal bedding cracks which are a common feature of the dike at this point in the pegmatite.

The largest pocket measured roughly about 14″ across at the bottom where it swelled somewhat from a narrow dimension at the upper part of only several inches. The next small pocket was essentially a vertical crevice with no appreciable swelling out. The third pocket, very small, was disposed horizontally but dipping toward the inside of the dike at an angle of about 45 degrees. This is apparently a continuation of the one which was cleaned out last week from inside the upper cut. This small pocket was of interest primarily for a mass of columbite which was intergrown with black-stained coarse muscovite and projecting into the pocket, yielding several more or less euhedral crystals.

The large pocket was lined with blocky perthite at the top upon which had grown flat morganite, subsequently found as shattered, recrystallized remnants in the pocket debris. None were found attached. Massive beryl was noted in the dike adjacent to the pocket (white). The pocket dirt had every appearance of ordinary topsoil in good tilth and pocket clay, unctuous, firm, and red-stained, [and] occurred only in thin layers on a sloping side as well as coating floor crystals of glassy euhedral pocket feldspar. The horizontal roof of the pocket (see diagram) yielded a magnificent matrix of quartz, glassy feldspar, muscovite (lepidolite on edges?), measuring about 12″ by 10″ and about 4″ thick. This showed no trace of envelopment by pocket clay and indicates the deposition control exerted over cookeite by gravity.

Sinkankas diagram image

Pocket at the Esmeralda Mine, North Main Workings, September 22–23, 1956. Click to enlarge. From the collection of Bill Larson.

 

Tourmalines were abundant in the larger pocket, a total quantity of about 5 lbs being recovered. There was a high percentage of flawless material but all suffered from rather dark inky colors. The principal hues were bluish-green, greenish-blue, claret, purple, and a peculiar purplish-gray. Several large pencils formed by aggregate-radiation, measured about ¾” diameter, swelling to as much as one inch at the termination (pedion), and about 4″ in length. Most were considerably smaller however, being single-crystal pencils ranging in size from needle-like prisms to those about ½” in diameter and several inches long. A number of crystals were obviously recrystallizations from broken segments and showed doubly-terminated crystals only an inch or less in length with a smooth, generally uncomplicated pedion, and the opposite end terminated by pyramids of various steepness. This end often shows cat‘s-eye material intruding to a short distance and are easily told by the tenacious coating of cookeite which defies ordinary methods of mechanical removal. These coatings are removed best by immersion in hydrofluoric acid.

Beryls found ranged from virtually colorless fragments to those of a light peach color. One peach crystal, probably of large size, had been shattered by mechanical forces in the last stages of pocket activity and showed regrowths on fracture faces upon ail pieces. The largest piece was a corner of a prism which would have measured, had it grown to its euhedral best, about 4″ tall and about the same in diameter. This piece, as well as several others, had ingrown tourmaline crystals upon the faces.

Quartzes were not large and followed the habits of previous finds in that they showed an interior of smoky, citrine, or somewhat straw-colored material, overgrown with faces showing much included material. Several were quite smooth however, and of a pale citrine hue. In addition to the fairly euhedral crystals lining the pocket walls, the usual collection of flat and distorted crystals grown from shards were obtained.

A considerahle quantity of exceedingly sharp glassy feldspar crystals were obtained also, seldom showing more than several faces as is the usual case. Some were coated with cookeite, especially those found in the bottom of the pockets. The larger pocket had one very large single crystal attached to one wall which measured 4″ wide and about 6″ in length. The others averaged considerably smaller however.

Columbite has been mentioned, the largest crystal noted being about 2″ in length and about 1″ in width. Others seen measured about 1″ in length and less in width and were tabular. The prism sides were striated and the terminations either to a point or flat with modifying faces on the ends.

Esmeralda Mine

Refer to topo map no. Mesa Grande USGS 7.5 Edit[ion] 1949

The Esmeralda Mine is mentioned by Kunz. It is supposed to have produced some morganite beryl, one specimen of which was said to have been sold for $600.00 and to have consisted of a large quartz crystal surrounded at the base by several morganite crystals. The production of gem tourmaline has always been reputed to be very small.

The mine was visited on Sunday 11 March 1956 and the entire day was spent exploring the rather extensive pits, prospects and underground workings. The mine is reached by taking the Lusardi Truck trail where it leaves Mesa Grande schoolhouse and descends into a valley southward. The road is tar for the first half mile, then changes to dirt. In about 3.2 miles and after numerous gate openings, it terminates at a locked forestry service gate which marks the border of Cleveland National Forest. Just before this gate is a meadow to the left upon which can be seen a pair of dim tracks; these are taken and followed until the top [where] a shallow knoll is reached. The car is parked and below the crest to the north can be seen two more shallow brushcovered knolls with open cast workings visible on their tops and sides.

Knolls photo image

This image from August 2011 shows knolls dotted with workings. The very distant mountain range is home to the Palomar Observatory. Click to enlarge.

 

The first knoll contains several shallow pits exposing a virtually horizontal pegmatite of simple composition which varies from a thickness of several feet to as much as ten on its eastern extremity. At this point can be see a deep trench running from east to west which exploits the ledge underlying the knoll and which is so close to the surface here that only a thin veneer of topsoi1 covers it. This ledge is barren in appearance but shows gatherings of very large shattered, black tourmalines. A piece of euhedral glassy pocket-type feldspar picked up at the open cut shows that at least one pocket of sorts was encountered here. There is no evidence of lepidolite or pocket clay and a mineralized streak as such is not in evidence.

The second knoll overlooks the [name omitted] Valley to the left and bears upon its summit and flanks the extensive workings and prospect pits of the Esmeralda Mine proper. A downhill bulldozer firebreak trail exposes the crest of the principal pegmatite which, as far as can be gathered from the confusing evidence available, must be nearly vertical in dip with possibly a component toward the east of about 10 degrees. The surface exposure shows at that point a width of nearly 15 feet. The strike is northeast–southwest and the exposed length appears to be at least ¼ mile. The numerous openings are upon this dike near the summit of the knoll but a series of others, below the crest to the south several hundred yards, although on the same general line, may be upon a parallel dike. Exposures are clear only on the summit of the knoll.

The northernmost workings are on the northern side of the knoll amid heavy brush and are invisible from the south. They consist of a deep vertical shaft with several laterals but it is probable that originally only a prospect pit existed at the summit which was later undermined by tunneling from beneath. There, are two main adits, one above the other and extending in an easterly direction to intercept the dike. Near the opening of the vertical shaft is much lepidolite, broken euhedral quartz, blocky feldspar, etc. Examination of the interior shows evidence that the dike is a vertical one since no, clear lamination exists. The mineralization is confused and irregular with perhaps greater concentration on the northerly side.

The next extensive set of workings is further south and those which are first encountered along the bulldozer trail Fire pits are to be seen here, all driven in as laterals to intersect the dike except one to the south which was tunnelled in for about 20 feet. Several pits are debris- and brush-filled. The mineralization here is relatively simple and specimens examined on the dumps indicate that pocketing was vuggy with mainly quartz crystals being produced. The tunnel itself shows an extremely uninteresting assemblage of ordinary pegmatite constituents with little sign that further development would produce anything worthwhile.

John Sinkankas’s macro sketch of the Esmeralda Mine layout, March 11, 1956. Click to enlarge. From the collection of Bill Larson.

 

Passing further to the south and downhill, a series of pits and tunnels, some partially slumped, are also encountered. There are about six distinct sets of workings. The pegmatite here partakes of the same uninteresting character of the last mentioned. Considerable quantities of rock were removed here but all evidence on the dumps indicates nothing worthwhile was obtained.

In general, the three sets of workings on the main dike show a progressive increase in mineralization from south to north reaching a climax at the most northerly set where lepidolite is abundant. Some lepidolite was noted in the middle set of workings but appeared to have originated as float material and led to one pit being excavated but probably with little result.

Minerals noted consisted of biotite in thin blades, some as much as 24″ in length in graphic granite and so arranged as to subdivide certain portions of the dike into fairly regular blocks of about 4″ in diameter. Much blocky euhedral feldspar of pure white color and perthitic is to be seen associated with milky and glassy quartz. Muscovite is not abundant, except locally near central units. The northerly pit shows considerable quantities of completely altered spodumene in lathlike crystals reaching as much as 8″ in length. Cleavelandite is abundant in central units where it fills interstices between coarse grains of quartz and feldspar. Blue tourmaline of a rich greenish-blue color was noted in small prisms here and there but usually adjacent to or inclosed in massive granular lepidolite. Very little of the latter mineral was noted in the form of coarse blades or fringes on muscovite; it seems primarily to appear as aggregates of small booklets. In the northern opening, it showed numerous instances where large tourmaline or spodumene crystals were enclosed and subsequently completely altered. One specimens was seen containing a tiny pink tourmaline.

Esmeralda Mine Notes

A Small Beryl Pocket

A small beryl pocket measur[ed] about 5″ across and about the same in depth but shaped like an avocado with its point down. Lined with very dark smoky quartz adherent to similarly colored material forming a lens in massive blocky perthite of a white color. Near the right and below, was seen a lens of massive white beryl which undoubtedly contributed the raw material for the morganite extracted from this pocket. The morganite was peach-colored.

Pocket contents were much shattered although enclosed in what was obviously fairly undisturbed rock. When opened from the bottom, the contents consisting of much loose mica scales varying in size from 1/16″ to 1/8″ as well as shards of quartz and beryl poured out into the opening below. No clay in evidence. All of the morganite showed old fractures indicating two large crystals had shattered but all crack surfaces were re-healed and pieces no longer fitted together snugly. A considerable number of thin shards of quartz, also recrystallized, were present as well as one or two euhedral crystals of deep smoky color and showing a thick layer of inclusions of white color on certain faces. Absolutely no tourmaline was found but no black crystal intruded into this pocket. Lepidolite of a faded color was frequent in loose round aggregates in the center of the pocket, mostly covered with a thick coat of cookeite. One small group of cleavelandite was also encountered.

Out of a pocket this small, a full handful of morganite crystal fragments were obtained, the largest being almost two inches across and showing several quite smooth but not glassy faces.

In relation to the other pocket, this one was along about the same line of mineralization but offset.

In this connection, it is worthwhile mentioning that mineralization in this section of the dike occurs along a chain of seams between relatively uninteresting pillow-like masses of coarsely granular feldspar and muscovite plus black tourmaline. If we can imagine a series of elongated pillows arranged with their long axes parallel but intermeshed in irregular order, we would have a fairly good idea of the disposition of the mineralization which occurs in the spaces between the pillows. The long axes of the “pillows” appears to be horizontal and parallel to one of the dike walls.

Sinkankas diagram image

John Sinkankas’s detailed sketch of the Esmeralda Mine layout, March 11, 1956. Click to enlarge. From the collection of Bill Larson.

 

Pocket Configuration

With the removal of capping rock from a pocket which had yielded some blue tourmaline, curious coated citrine crystals a and several specimens of beryl (morganite and goshenite, aquamarine), as well as a much-altered group of columbites, the limits and surrounding mineralization were made plain.

The pocket had originally formed along a crack running in an essentially vertical plane with some corkscrewing and enlargement at the top. The shape was roughly discoidal but with the upper edge flattened. This crack had then been enlarged by subsequent earth movements until it was several inches wider and filled with grayish topsoil containing much organic matter. Loose clay, if any, had been leached away. The walls of the crack showed on one side mainly blocky perthite with individual crystals reaching about a foot in maximum dimension. On the other side, quartz was far more prominent and appeared in one section as an interlamination between feldspar, massive beryl, and mica. One large crystal of pale morganite, shattered unfortunately, was found adhering to the wall and was rooted into the beryl mass which measured at least a foot along its length. Where the beryls penetrated the feldspar the morcanite color was lost and white took its place as well as a faint aqua color.

In summary, the pocket was lens-shaped but oriented vertically, but with one p1ace near the top where it opened out into a shelf-like extension. At this thickened place, large quartzes and feldspars had formed as well as beryls. Euhedral tourmalines, doubly terminated came from this are also, probably, but were found in the loose topsoil near the bottom of the crack leading to the pocket. A number of the tourmalines were coated with cookeite which was common in this pocket but others were quite clean. Many showed re-healed fractures and spurious terminations resulting therefrom.

Pocket filling appeared to be a much decomposed feldspar, of a rich brick-red color as evidenced by deposits still adhering in favorable places. Permeating this pocket feldspar was much mica, probably cookeite, in minute silvery scales oriented at random and so abundant that the feldspar was given an unctuous feel. Broken and whole crystals of tourmaline were found in this material indicating its formation subsequent to that of tourmaline. A rarely-encountered event in the county is the occurrence of tourmaline implanted on beryl but not included therein. However, the most striking feature is the abundance of massive beryl in the feldspar/quartz central unit of this dike.

 

Approach to Pegmatite photo image

The approach to a cut in the main pegmatite from a visit in August 2011.

 

 

Sinkankas Notebook

One Comment

    1. Edward Boehm says:

      This is a fabulous wealth of historical information on the Esmeralda. Thank you for sharing so much of John Sinkankas’ detailed notes and sketches from your personal collection. I felt as if I were there with John exploring the pegmatite over 60 years ago.

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Sinkankas Notebook

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