Road Cut Mineral Occurrences of St. Lawrence County, New York:

Yellow Lake Road Cut Occurrences

 

 

     

                  "The Heart" Calcite                                 Caclite on Marble                                           Twinned Calcite                                       Dolomite on Calcite

 

by Steven C. Chamberlain and Michael R. Walter 

 

Part I, Yellow Lake North

This is the second in our series of articles on significant road-cut localities for mineral specimens in St. Lawrence County, New York. The Yellow Lake road-cut produced thousands of excellent specimens of calcite and dolomite starting 40 years ago, although it has not been particularly productive for the past several decades.

 The Yellow Lake road-cut is on the edge of a small rise about 1.1 km northwest of the northern tip of Yellow Lake in the Town of Macomb (Fig. 1) The road-cut is on the west side of County Rt. 10 about 6.2 km north of the intersection of Rt. 10 and Rt 3 near Oxbow. The road-cut faces an open field on the east side of Rt 10, north of the intersections with Scotch Settlement Road and Hall Road, but south of the intersection with Robinson Road. It appears on the upper left corner of the Natural Dam quadrangle in the USGS 7.5 minute topographic series (1961). The calcite specimens produced from the open cavities at this road-cut are distinctive.

 

History

 

This locality was appears to have resulted from the widening of County Rt 10 that occurred in the early 1960' s. Although not the first collectors, George Robinson and Mike Hubinsky noted cavities of interest in the road-cut in the late fall of 1964 while returning to SUNY Pots dam from a day trip to the Rossie Lead mines. During their visit to SUNY Potsdam in March, 1965, Robinson persuaded his parents to visit the locality on a Saturday, and by Sunday afternoon about 500 pounds of specimens had been recovered. Hubinsky and Robinson returned the next weekend and collected another 500 lbs of specimens. Also in the 1960s, John Pietras of Rome, NY, collected hundreds of high quality specimens from the locality. Local collectors, including Ivan McIntosh, Bob Johnson, and Charlie Bowman collected at the locality during this period, as well as many others, since the locality was listed as locality 19 in Minerals of the St. Lawrence Valley (Robinson and Alverson 1971).

 The evidence at the locality as it appeared in March, 2004, (Figs. 2,3) supports the reports of these early collectors that most of the exploited crystallized cavities were between the pavement and the vertical portion of the road-cut and were at, or below, the level of the paved surface of the road. These cavities were filled in by the highway department long ago. There is every possibility that future exploration could uncover additional mineralized cavities (Figs 4,5); indeed recent collecting has yielded fine specimens of calcite and dolomite (Figs.20, 21).

 

 Geology

 

The locality sits on the eastern flank of a northeast-southwest trending ridge that is part of overall fold patterns in the area north of the village of Oxbow. The rock itself is a complex assemblage dominated by Grenville marbles and other metasedimentary and metavolcanic units (Van Diver 1976, 1980). Plastic flow in the marbles has resulted in complex banding with silicate lenses, rods, and boudin structures. Tectonic activity, possibly related to that which formed the nearby Rossie lead mines (Robinson et al. 2001), has produced fractures and slickensides, providing an avenue for later mineral transport and deposition.

 The Yellow Lake road-cut exposes fracture-filling mineralization in the Precambrian marble (Isachsen and Fisher 1970). Locally, the white marble has complex interrelationships with dark gray Cambrian Pots dam sandstone, that contains altered clasts up to several centimeters (see Brown 1983, for a discussion of the Precambrian/Cambrian unconformity). The age of the crystallized minerals in the fractures in unknown, but is certainly much younger in age than the host rock.

 

Minerals

 

Calcite, CaC03' occurs in two generations of distinctive habit (Figs. 6,7). The first calcite crystals to form occur as white scalenohedral crystals up to 2 centimeters and as white scalenohedral {21-31} crystals up to 15 centimeters terminated by small rhombohedral faces {lO­II} both formed directly on a matrix of fine-grained marble (Figs. 9, 10, 11). The larger crystals typically have a dark brown scalenohedral core. Both forms of these early scalenohedral calcite crystals are symmetrically developed. A later generation of calcite consists of sheet-like parallel growths of colorless to white to medium gray scalenohedral crystals {21-31} with pale yellow tips showing rhombohedral faces {10-11} (Figs. 8, 13, 14, 15). Individual crystals may be up to 10 centimeters tip-to-tip. Usually there is a thin rhombohedral zone containing microscopic sulfide crystals separating the main crystal from the pale yellow tip. A few of these scalenohedral crystals are twinned on (0001), but most are not. Sometimes the larger scalenohedral crystals are cavernous with myriad smaller oriented scalenohedral crystals with pale yellow tips lining the surfaces (e.g. Fig. 10). Most of the scalenohedral crystals of this generation show growth distortion of the scalenohedral faces such that two of the opposite faces are large and four of the faces are small on each end of the crystal (Figs. 12, 18) but some are symmetrically developed (Figs. 16, 17). Pale gray phantoms are occasionally encountered inside colorless or yellow scalenohedral crystals. Plates of calcite and dolomite crystals up to 40 centimeters square, perhaps larger, were recovered.

 

Dolomite, (Ca, Mg)C03' forms lustrous, creamy white to tan-colored, curved rhombohedral crystals up to 1 centimeter. They occur as masses attached to calcite (Figs. 20, 21, 22), sometimes as an epitactic overgrowth (Fig. 19). The largest clusters of dolomite crystals exceed 10 centimeters in maximum dimension. Some specimens show evidence of an early phase of dolomite formation, now largely altered to goethite, and the more typical later phase with the dolomite formed on the second phase of calcite.

 

Goethite, FeO(OH), occurs as a thin surface coating on some calcite crystals and as earthy masses up to several centimeters replacing pyrite.

Graphite, C, occurs as shiny black plates up to 1 millimeter, usually associated with quartz crystals, but sometimes embedded in minute, late-stage calcite crystals.

Marcasite, FeS2' commonly occurs as microscopic needles and plates along internal planes within calcite crystals. Some of these minute crystals are twinned. Marcasite also occurs as flattened cockscomb arrays of crystals up to several mm in masses with cub octahedral pyrite crystals.

Pyrite, FeS2' rarely occurs as microscopic cubes inside and on the surface of calcite crystals. Cuboctahedral and octahedral pyrite crystals up to 3 millimeters form crystallized masses scattered among the calcite crystals (Fig. 23). Almost all of these have completely altered to earthy goethite and have lost any trace of the original pyrite crystal faces.

Quartz, Si02' occurs as small transparent prismatic crystals to 1 centimeter in length. Generally the positive and negative rhombohedral terminations are equally developed (Fig. 24). These crystals often contain plates of graphite.

Siderite, FeC03' occurs rarely as rhombohedral crystals up to 1 centimeter with calcite (Fig. 25). Often these are coated with a. thin layer of goethite.

 

Paragenesis

 

    The first mineral to form was calcite either in small white untwinned scalenohedra tending to lie sideways on the matrix or in larger white scalenohedral crystals with dark brown cores that are oriented with the c axis approximately perpendicular to the matrix. Masses of pyrite and marcasite formed toward the end of calcite crystallization. A second generation of calcite formed later on top of the first generation. These calcite crystals are colorless to white to medium gray and form sheets of parallel scalenohedral crystals joined at the girdle. There seems to be no epitactic orientation between these sheets and the underlying large scalenohedral crystals of the first calcite generation. In general the orientation of the scalenohedral crystals in each sheet is with the c axis parallel to the surface of the matrix. More pyrite and marcasite masses formed with this second generation of calcite. There was a pause in calcite crystallization during which microscopic, unoriented crystals of marcasite, and more rarely cubes of pyrite, formed sparsely on the rhombohedral terminations of the sheets of scalenohedral calcite crystals. Calcite of a pale yellow color then continued to form giving a colored tip to the scalenohedral crystals with rhombohedral terminations. Quartz and graphite formed just at the end of the crystallization of the second second general phase of calcite crystallization and occurs in localized regions on some specimens. Dolomite formed after calcite crystallization had stopped. Some of the dolomite is epitactic on rhombohedral or scalenohedral faces of the underlying calcite. Much of it formed as unoriented curved masses of crystals on the calcite. In some specimens the dolomite is partially embedded in the second phase of calcite indicating overlap of the periods of crystallization. Some specimens also show a minor earlier phase of dolomite formation, subsequently heavily weathered and replaced by goethite. The final stage in the paragenesis saw the oxidation of most of the masses of sulfides to earthy goethite and the formation of thin coatings of goethite or botryoidal calcite on the surfaces of other minerals.

 

Origin

 

The crystals of this occurrence formed in fractures and solution cavities in the Precambrian marble. The presence of graphite crystals on and embedded in quartz crystals indicates that the mineralization is relatively recent and resulted from downward percolating meteoric water that dissolved portions of the overlying marble and redeposited it in the fractures. The components of the calcite and dolomite are almost certainly from the overlying marble itself. The graphite crystals have been freed from the dissolved marble and have fallen and been carried downward through the fractures. The source of the silica in the quartz that crystallized with the graphite is silicates in the marble that are metastable at surface conditions and are weathering. Organic molecules introduced into the ground water from the roots of plants in the overlying soil zone have held the silica in solution (see Bennett and Siegel 1987; Chamberlain 1988) for several meters until bacterial attack reduced the average molecular weight of the organic complexing agents below the point where they could hold silica in solution and the quartz precipitated. The fact that the quartz crystals are largely transparent and flawless, except for the included graphite crystals, suggests that the transport of silica by organic complexing agents and its subsequent release were slow processes resulting in gradual formation of the quartz crystals from subsaturated solutions.

The dissolution of marble or limestone by ground water higWy charged with carbon dioxide by plants in the soil zone and then reprecipitation as temperature changes cause degassing of carbon dioxide from the solution is the same mechanism that forms limestone caverns. The processes whereby iron sulfide, principally pyrite, disseminated in the marble is oxidized, but then later reduced and reprecipitated as marcasite and pyrite are less clear. Normally, the oxidative weathering products of pyrite in marble are goethite and gypsum. At this occurrence, both marcasite and pyrite formed in oriented bands of microscopic crystals on the rhombohedral faces just before the final stages of calcite crystallization and macroscopic crystals of pyrite and marcasite formed concurrently in the same sulfide crystalline mass. Whatever the process, these

data indicate that the conditions for precipitation were right at the boundary between the large pyrite stability field and the much smaller marcasite stability field, that is, that the precipitating solutions were slightly acidic.

The most recent conditions have been oxidizing and most of the masses of iron sulfides have completely altered to earthy goethite. Thin coatings of goethite also formed on some of the calcite crystals. Minor calcite precipitation has continued in the form of thin stalactitic overgrowths of tan calcite on some of the calcite and dolomite crystals (e.g. Fig. 18).

 

A Note on Specimens

 

Very large numbers of distinctive and desirable specimens were collected at this locality. Good examples frequently surface as older collections are recycled. Contemporary collectors should note that some specimens from this occurrence were briefly dipped in dilute hydrochloric acid to remove goethite stains and thin crusts of stalactitic calcite-this practice is common among local collectors. Many of the calcite specimens, however, have crystals with natural faces of very high luster. Careful inspection of cleavage surfaces on the back of specimens will usually indicate whether the specimen has been subjected to acid treatment during cleaning.

 

Accessibility

 

This road-cut is accessible for collecting; however, the large vugs below the road surface have been filled in the interests of vehicular safety. Our recent collecting indicates that further exploration is likely to yield more mineralized seams and vugs that may produce additional interesting specimens.

 

ACKNOWLEDGEMENTS

 

The authors are grateful to Dr. George Robinson or Michigan Technical University for sharing some of the early history of the occurrence and to Brian Corzilius of Ithaca, NY, for preserving the material from the Pietras Collection. We thank Mike Hawkins of the New York State Museum for providing access to specimens from this locality for examination.

 

REFERENCES

 

Bennett, P. and Siegel, D. I. 1987. Increased solubility of quartz in water due to complexing by organic compounds. Nature 326:684-686.

Brown, C. E. 1983. Mineralization, mining, and mineral resources in the Beaver Creek area of the Grenville Lowlands in St. Lawrence County, New York. U.S. Geological Survey Professional Paper 1279.

Chamberlain, S. C. 1988. On the origin of "Herkimer diamonds." Rocks and Minerals 63:454.

Isachsen, Y. W., and Fisher, D. W. 1970. Geologic Map of New York, Adirondack Sheet.

University of the State of New York, The State Education Department, Geological Survey.

Robinson, G. and Alverson, S. 1971. Minerals of the St. Lawrence Valley. Privately published.

Robinson, G. W., Dix, G. R., Chamberlain, S. C., Hall, C. 2001. Famous mineral localities: Rossie, New York. The Mineralogical Record 32: 273-293.

Van Diver, B. B. 1976. Rocks and Routes of the North Country. Humphrey Press, Geneva, New York.

Van Diver, B. B. 1980. Field Guide to Upstate New York. W. F. Kendall/Hall Publishing Company, Dubuque, Iowa.

 

 

by Michael R. Walter and  Steven C. Chamberlain

 

Part II, Yellow Lake South

Recently we published a paper on the Yellow Lake Road Cut (Chamberlain and Walter 2006).  In the summer of 2006, one of us (MW) encountered an extensive series of mineralized pockets on the same ridge, a short distance south of the classic locality.  Over a period of two weeks, hundreds of noteworthy specimens were recovered.  We report this new set of pockets as the road cut at Yellow Lake South (YLS) because it has a suite of minerals and crystal habits that are distinct from those at the original locality, which we will refer to as Yellow Lake North (YLN).  Moreover, we are able to report and illustrate the actual extraction of significant pockets of specimens—something we were unable to do for YLN.  Comparing and contrasting these two, nearby occurrences provides an interesting insight into fracture-filling occurrences in the Grenville marble.

 

LOCATION

        The occurrence is a road cut on the edge of a small rise 1.1 kilometers northwest of the northern tip of Yellow Lake in the town of Macomb (fig. 1).  The road cut is on the west side of County Route 10, 6.2 kilometers north of the intersection of Routes 10 and 3 near Oxbow.  The road cut faces an open field and small house on the east side of Route 10 at 44° 20' 22"N, 75° 36' 14"W, south of its intersection with Robinson Road and north of its intersection with Hall Road.  The occurrence appears on the upper left corner of the Natural Dam quadrangle in the U.S. Geological Survey’s 7.5-minute topographic series (1961).  The newly excavated pockets sit about fifteen meters south of the older locality.  The relationship of the two occurrences is shown in Figure 2.

 

HISTORY

      What follows is Mike Walter’s account of the discovery and excavation of the pockets at Yellow Lake South.

        On the eve of the publication of our paper on Yellow Lake, I decided to visit the locality once again before it came to public notice.  I arrived the morning of July 14, 2006, to find that the county department of transportation has regraded the berm and completely filled in the excavations of the previous year.  Had I not been waiting for the arrival of my Father for a day’s joint collecting, I would have undoubtedly gone elsewhere right away.  As it was, I started exploring the edge of the ridge along the road and about fifteen meters to the south, I noticed a small stringer of calcite with a white crumbly powder that appeared to be barite.  Further inspection revealed a half-centimeter vertical vein running through an otherwise barren marble and into the dirt at the base of the road cut.  Digging began here and at a depth of about a meter, the vein had widened to about ten centimeters of massive gray calcite that was easy to remove.  I encountered soft weathered marble about a half meter deeper with a second vein of calcite running parallel to the road and intersecting the vertical vein I had been following (fig. 3).  As sections of the weathered rock were removed, I found gray clay and brown, rusty sand filling the seams between the pieces.  The rock slabs seemed flatter than normal and had a druse of tiny calcite crystals coated with gray clay on their undersides.  The opening to the first chamber was indicated only by the presence of calcite crystals in the clay and taps with my four-pound crack hammer revealed the enticing sounds of a hollow space. Within minutes I had broken into an opening approximately a meter in diameter (fig. 4).  The base was filled with a mound of gray glacial clay and the ceiling held a single large inverted yellow rhombohedral twin of calcite among other smaller crystals.  The crystals that were still attached to the walls and ceiling of the chamber were coated by a thin layer of wet clay.

        This was the largest pocket I’d thus far discovered at the either site, and I was unexpectedly surprised by how accessible it was.  Dad arrived in late morning and began to pack the specimens that had been accumulating in flats around the opening.  All the specimens were covered with more or less clay, but were recognizable as crystals, not wall rock.  Twenty flats of crystals were excavated by this point in time and I had not even begun the pocket extraction.

        We returned with great enthusiasm and expectations the following day to begin removing crystals from the chamber, which we will refer to as chamber one.  I began by collecting all the lose crystals and clusters sitting on and in the mound of glacial clay.  Early in this process, I lifted out a 12-cm single scalenohedral crystal with a nice ring of epitactic dolomite girdling its midsection (fig. 15).  The piece was a surprise because most of the material I was removing appeared to be very weathered.  The twin hanging from the ceiling was also a very nice specimen, but otherwise in the twenty-seven flats of crystals we removed that day, there were no more than ten nice specimens.  My disappointment about the weathered calcite was balanced by the discovery of several large barite crystals along the bottom of the chamber.  These fragile crystals were completely packed in heavy clay and were almost impossible to remove without being destroyed.  Some were up to eighteen centimeters, and the nicest, and only doubly terminated piece (fig. 11), was excavated from the very base of the pocket.

        On day three, I continued to remove specimens from the chamber, and Dad continued to pack them in flats.  As the empty cavity was explored, it was clear that the chamber did not extend deeper into the wall, but there was more clay-filled open space toward the road.  Unfortunately, this space extended under a rectangular boulder several tons in weight.  During the night it had shifted three or four centimeters and was therefore loose and movable.  Although I usually have chains and a come-along for moving just such obstacles to progress, I did not pack them that day.  The only other solution was to prop a steel pipe between the boulder and the wall.  During this phase my Dad was promoted to “boulder-watcher-in-chief” as I worked on removing the plug and exploring what was beyond.  Next, a crowbar was used to unceremoniously yank out the large clay plug.  Although this clay was filled with many crystals and a large piece of barite with crystals coating one side (fig. 13), it was nearly forgotten as the interior of the second chamber was now clearly visible.  Our third day was turning into a red-letter event.

        Like the first chamber, this opening had an enormous pile of gray clay on the bottom.  In this chamber, however, all the crystals from the ceiling had fallen about a half-meter into the clay below without damaging each other.  As I began pulling pieces indiscriminately off the pile and bringing them out into the light, I was delighted because the specimens seemed to be of excellent quality, but confused because the habit of the calcite crystals was very different.  I removed piece after piece of well crystallized calcite, but all showed a completely different habit from the predominantly scalenohedral form of the YLN specimens found a stone’s throw away.  These crystals were of equant, ball-shaped habit with dominant rhombohedra and most showed Rossie twinning (fig. 16).  Some were “nest twins” previously common at the Oxbow road cut (Walter and Chamberlain 2008) (fig. 18).  Moreover, although the crystals had pale green phantoms and oriented inclusions of either marcasite or pyrite, they did not show the bright yellow calcite overgrowths at their tips so distinctive of virtually all specimens from YLN.  Finally, the individual crystals seemed much larger, to ten centimeters, and were in clusters up to thirty centimeters or more.  Most of the crystals were translucent yellow and some had minor overgrowths of dolomite.  Although adjacent to the first chamber, and about the same size, a meter by a meter by a meter, the contents of chamber two were significantly different.

        I removed the crystals in flats or as individual pieces.  Work continued at a feverish pace due to the instability of the overlying rock.  I felt as though I was a mouse working in an egg shell with a brick sitting on top of it.  No attempt was made to try and remove any of the crystals from the walls.  Once all the specimens in the pile of clay had been removed, I was “out of there”.  Even so, we managed to cover much of the floor of my Father’s van and the surrounding ground with approximately thirty flats and loose specimens of great potential (fig. 5), which we took home and added to the growing pile (fig. 6).

        Before leaving, we decided that abandoning the precariously balanced boulder was not appropriate, so the hole was filled, the pipe pulled out, and we watched as the boulder slowly shifted toward the opening of the first chamber.  We finished the job by completely filling in the excavation.

        Although it was our intention to conclude the dig, which is why we filled in the excavation, as I washed some of the specimens, their quality suggested our ending work was premature.  So days four and five were spend digging down to chamber two on the opposite side of the now toppled and stable boulder.  The weather had turned really hot, and no specimens were recovered on these two short days of digging.  We did however open a sand-filled, half-meter pocket almost at ground level, but every crystal inside was too weathered to save.

        Day six found me sitting in chamber two removing the clay and rock in the search for the bottom of the opening.  Once I reached the rock at the bottom, I found it easily removed in fairly large blocks and plates.  Once there was enough room to swing a hammer, I inspected the walls more carefully and discovered what became chamber three.  Unlike the first two chambers, this one was a narrower opening with no crystals on the floor, but instead with walls lined by well-formed groupings of modified scalenohedral crystals in parallel growth (fig. 7).  The habit of calcite crystals in this chamber was reminiscent of those found in the pockets of YLN.  Although I couldn’t quite see down the length of this chamber, I could feel by extending my arm that the walls and ceiling were all lined with sharp crystals.

        Day seven was spent emptying chamber three with a hammer and chisel.  I recovered smaller groupings of crystals with nice pale green phantoms and bands of inclusions of acicular iron sulfides.  When the walls and ceiling of the chamber were striped, I returned to removing rock and clay from the bottom of chamber two.  By this time, the process of getting debris out of the pocket system required a bucket on a rope.  By the end of another heat-shortened day, there were indications of a possible fourth chamber below, behind and somewhat to the north of chamber two.  The north wall of chamber two was composed of soft, rotted marble and clay which simply fell apart when scraped.

        On the morning of day eight, I broke through the north wall of chamber two into chamber four.  Figure 8 shows the opening into chamber four created with the thrust of a screw driver. This opening quickly widened into the largest of the chambers, two meters long, a meter and a half wide and an unknown depth.  Like the others, there was a large mound of glacial clay on the floor.  On this clay sat several large clusters of coarse doubly-terminated scalenohedral calcite crystals with no modifications and no twinning.  They were gray brown and not of collector quality.  The best specimens from this day’s digging came from the soft rock barrier between chambers two and four.  Near the top of this barrier was the area where the barite seam intersected the opening of chamber two.  I was hopeful that conditions might have been right for the formation of combination specimens of calcite and barite.  My efforts were indeed rewarded by my finding such specimens, but only a very few, with only one being noteworthy (fig. 12).  When I encountered this specimen, it was a wad of clay with protruding barites.  I couldn’t tell whether the barites were lose or attached.  On a hunch, this glob of crud was taken to the surface and Dad was asked to just sit it in a box and not even risk wrapping it.  Once it was hosed off at home, I realized it was indeed a combination specimen of barite and calcite.  Otherwise most of the barites were loose and evidence that they actually came from a Yellow Lake calcite chamber was scant.  Many of the lesser calcite specimens from this barrier had the unusual feature of having white to brown, almost earthy, barite as a selective coating on skeletal calcite crystals.  Barite was also sometimes found in fractures or internal skeletal layers, creating interesting phantoms.

        Toward the end of day eight, the land owner’s wife visited the locality and, impressed by the size of the cavities we had excavated (fig. 9), requested that we conclude our collecting because even though we had their permission, they had become concerned about our safety and the safety of others who commonly drove ATVs down this stretch of road.  We immediately complied with her request and filled the entire area we had excavated back to grade.

        A summary drawing shows the position of the four chambers and their relationship to the road and the face of the ledge (fig. 10).

        

GEOLOGY

        This locality is on the eastern flank of a ridge that trends from the northeast toward the southwest and is part of an overall folding pattern in the area north of the village of Oxbow.  The rock itself is a complex assemblage dominated by marbles and other metasedimentary and metavolcanic units of Grenville age (Van Diver 1976, 1980).  Plastic flow in the marbles has produced complex banding of silicate lenses, rods, and boudin structures.  Tectonic activity, possibly related to that which formed the nearby Rossie lead mines (Robinson et al. 2001), has produced fractures and slickensides, providing an avenue for later mineral transport and deposition.  Both the Yellow Lake North and Yellow Lake South road cuts expose fracture-filling mineralization in the Precambrian marble (Isachsen and Fisher 1970).  At Yellow Lake South, the various chambers clearly represent significant solution cavities formed by the action of unsaturated ground waters at some time in the past.  More recently saturated ground waters resulted in the deposition of significant mineralization on the surfaces of the cavities.  Glacial clay was forced into the open spaces of the chambers probably during Pleistocene glaciation.  At some time in the recent past, unsaturated ground waters again flowed through the chambers causing etching and oxidative weathering of the sulfides. 

 

MINERALS

        Barite, BaSO4, occurred as white, opaque crystals to 18 centimeters (fig. 11) in chambers one and two.  Some specimens show parallel growth.  Crystals have the basic form of prisms and pinacoids, but the surfaces are far from smooth with a frosted to feathery texture (fig. 11, 12 and 13).  Many terminations have a feathery texture.  Rarely barite crystals have poorer crystal form and smooth surfaces.  A few groups of barite crystals weighed more than 30 pounds (fig. 13).  More rarely, barite occurred as coatings on calcite crystals and filings within calcite crystal voids at the intersection of chambers two and four (fig. 14).

        Calcite, CaCO3, occurred as yellow crystals, often twinned in several distinct habits.  Individual crystals to 15 centimeters and clusters to 30 centimeters were collected.  None of the calcite crystals from this occurrence had the dark brown cores typical of specimens from the nearby classic site.  Variable evidence of surface etching by acidic ground water is visible on calcite crystals removed from the walls of the chambers, but calcite crystals that were fully encased in gray glacial clay show no such surface etching.  The habit of calcite crystals was distinctive in each chamber as were certain associations, for example only chambers 1 and 2 had dolomite overgrowths.  For this reason, the calcite crystals in each chamber will be described separately.

        Chamber one: The entry into chamber one had calcite crystals with scalenohedron {21-31} without twinning.  Within chamber one, calcite crystals were found both as modified scalenohedra, {21-31} terminated by rhombohedra, {10-11} to 12 cm (fig. 15) and equant, ball-shaped crystals with nearly equal development of the scalenohedron {21-31} and rhombohedron {10-11} to 10 cm.  Many of the scalenohedral crystals show major development of alternate scalenohedral faces with minor development or deletion of  the other faces.  This gives the crystals the appearance of steep rhombohedral crystals with angles close to {50-52}, however close inspection reveals that all of them are scalenohedral.  Only chamber one showed a mix of calcite crystal habits.

        Chamber two: Calcite crystals from this chamber constitute the majority of collector-grade specimens.  Almost all were complex twins on (0001) and parallel growths of crystals, both on and off of marble matrix, with ball-shaped habit characterized by nearly equal development of the scalenohedron {21-31} and rhombohedron {10-11} (fig. 16 and 17).  Individual crystals to 12 cm were recovered.  Orienting the crystals is made more difficult because the common difference in luster between scalenohedral faces and rhombohedral faces is absent in these specimens.  Only in a couple instances did these calcite crystals show color variation similar to the classic calcites from the nearby occurrence, including one interpenetrant  “nest” twin  on (0001) (fig. 18).  Some calcite crystals from this chamber show an unusual pattern of small white chatter marks along crystal edges (fig. 19).  These, however, are arrayed inclusions within the crystal and not a surface feature.

        Chamber three: Calcite crystals were still attached to the walls only in this chamber.  Modified scalenohedral crystals {21-31} with minor rhombohedral {10-11} modifications of the termination to 8 cm formed parallel growths similar in form to those from the classic occurrence nearby, but without the brown cores, color zoning, or dolomite overgrowths (fig. 20).  A few show classic scalenohedral contact twins on (0001).

        Chamber four: Although this chamber was not fully excavated, its crystals have the simplest morphology, consisting of parallel growths of simple scalenohedra in groupings to 30 centimeters. The crystals were all weathered with extensive dissolution from acidic ground waters and only one large cluster of crystals was preserved (fig. 21).  Like the crystals in chamber one, many of the crystals have an apparent rhombohedral habit close to {50-52}, but despite considerable dissolution from weathering, we believe these are actually scalenohedral crystals {21-31} with unequal development of the faces.

        Figure 22 summarizes the forms present on calcite crystals from the four chambers.  None of the twinning relationships are shown.

        Dolomite, CaMg(CO3)2, was encountered only in chambers 1 and 2 as groups to 5 cm made up of crystals to 1 centimeter (figs. 23, 24 and 25).  Both epitactic and random orientation of the dolomite on the calcite occur.  Some calcite specimens show clear evidence of two generations of dolomite.  Much of the first generation appears to have weathered away leaving imprints on the surface of the calcite crystals.  Some calcite crystals show both imprints of the missing first generation and pristine, unaltered second generation dolomite.

        Goethite, FeO(OH), occurs as an alteration product of marcasite and pyrite, both as euhedral pseudomorphs and as stains and coatings.

        Graphite, C, is present on many specimens as small flakes, often embedded within or on quartz (fig. 26).  Graphite also occurs in the surrounding marble (fig. 33)

        Marcasite, FeS2, occurs as oriented bands of inclusions of acicular crystals in calcite crystals, especially from chambers 2 and 3 (figs. 27, 28 and 29).

        Pyrite, FeS2, occurs in crystalline plates to 11 centimeters with individual cubo-octahedra to 0.5 centimeters, usually partly altered to goethite in chamber 2 (figs. 30 and 31). 

        Quartz, SiO2, occurs on many specimens as a late-stage deposition with graphite flakes and uvite crystals (fig. 32).

        Uvite, CaMg3(MgAl5)Si6O18(BO3)3(OH)3F, occurs as small green, yellow, and brown crystals and crystal fragments embedded in or on quartz (figs, 32-33.  It also occurs with graphite in the surrounding marble (fig. 34).

DISCUSSION

      The paragenesis appears to be similar in general plan to that we described for the Yellow Lake North Road Cut (Chamberlain and Walter 2006).  Calcite seems to have preceded dolomite in the deposition sequence.  Both marcasite and pyrite were precipitated, although at different times, permitting a change of conditions to move from the marcasite stability field to the pyrite stability field.  Like the Beaman Road occurrence (Walter and Chamberlain 2004), barite is present at this locality.  Our hypotheses regarding the origin of quartz from the breakdown of silicates in the marble and the role of humic acids from the soil zone in its transport are further supported by this occurrence with both uvite and graphite from the overlying marble serving as tracers indicating the source of the silica and fluids depositing the quartz.  It would appear that all the mineralization here resulted from the local action of downward percolating meteoric waters that dissolved some components of the marble and carried others along with the flow (uvite and graphite).  The deposition of calcite, dolomite, marcasite and pyrite would appear to be simple solution chemistry.  The deposition of quartz with wholly or partially embedded crystals of graphite and uvite indicates an enhanced mobility of silica that came from the breakdown of silicates in the marble that are metastable at the surface.  Organic molecules related to humic acids produced by plants in the overlying soil zone appear to be the means of enhancing the mobility of silica (Bennett & Siegel 1987, Chamberlain 1988).

        What strikes us as particularly interesting about this occurrence is the diversity of mineralization and calcite habits found in adjacent pockets. Calcite specimens from an extensive series of similar pockets at the Yellow Lake North Road Cut, extracted over decades of collecting, are remarkably similar in crystal habit, in zoning, and in accessory mineralization.  By contrast, each of the four chambers opened and excavated 15 meters away at Yellow Lake South has a different calcite morphology and set of associated minerals.  Although the mechanisms we are invoking to explain this mineralization would seem to be of regional scale, clearly the local control of crystallization has small spatial frequencies, varying markedly from one pocket to an adjacent pocket when conditions are appropriate.

        The intersection of these four pockets with a seam of barite mineralization provided very interesting barite specimens, which seem to have utilized the space in the solution cavities to crystallized, but interacted very little with the calcite in doing so.  We suspect the source of the barite is not the marble itself but other layers in the metasedimentary stratigraphy with original evaporite mineralization.

        The consistent presence of gray clay of glacial origin is a clear reminder of the fracture porosity of these rocks under the hydrostatic load of a thick ice overburden.  This just reinforces the reality that such solution cavities are both formed by dissolution and mineralized by precipitation from local ground waters.

        We have now examined four occurrences of calcite and accessory minerals in solution cavities in Grenville marble—Beaman Road (Walter and Chamberlain 2004), Yellow Lake North (Chamberlain and Walter 2006), Oxbow (Walter and Chamberlain 2008) and Yellow Lake South in this paper.  We are building a conclusion that the overall mechanisms involved in such mineralization, including sequential marble dissolution and calcite precipitation from meteoric waters, and the precipitation of silica, released from metastable silicates, as quartz, enhanced by humic acids from the soil zone are operating regionally, the details of mineral associations, order of deposition, and crystal habits are subject to local controls, probably both in time and space.  These localities are interesting not only because they produce display specimens, but also because they give us hints of the diversity of mineralizing process details in this PreCambrian terrane.

       

Acknowledgements

The authors thank the local land owners for allowing quite extensive excavations on their property.  We also thank Dr. Marian Lupulescu of the New York State Museum for analysis of the tourmaline, and Michael Hawkins for providing access to the NYSM Syncroscopy/AutoMontage system for taking the photomicrographs.

 

References

 

Bennett, P., and D. I. Siegel. 1987. Increased solubility of quartz in water due to complexing by organic compounds.  Nature 326:684-86.

Chamberlain, S. C. 1988. On the origin of “Herkimer diamonds.” Rocks & Minerals 63:454.

Chamberlain, S. C., and M. Walter.  2006.  Road-cut mineral occurrences of St. Lawrence County, New York.  Part 2: Yellow Lake road cut.  Rocks & Minerals 81:366-73.

Isachsen, Y. W., and D. W. Fisher. 1970. Geologic map of New York, Adirondack Sheet.  University of the State of New York, State Education Department, Geological Survey.

Robinson, G. W., G. R. Dix, S. C. Chamberlain, and C. Hall. 2001. Famous mineral localities: Rossie, New York.  Mineralogical Record 32:273-93.

Van Diver, B. B. 1976. Rocks and routes of the North Country. Geneva, NY: Humphrey Press.

______. 1980. Field guide to upstate New York. Dubuque, IA: W. F. Kendall.Hall.

Walter, M. and Chamberlain, S. C., 2004.  Road-cut occurrences of St. Lawrence County, New York: Part I – Beaman Road barite occurrence.  Rocks & Minerals 80:180-185.

_______. 2008 Road-cut occurrences of St. Lawrence County, New York: Part III – Oxbow road cut.  Rocks & Minerals (in press).

 

 

Specimens for Sale Here...   Calcite and dolomite form impressive clusters and make unique mineral specimens from this road cut occuance in St. Lawrence County, New York..  Calcite from Yellow Lake Road cut

 

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