Tri-State vs. Trend

 

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A Guide to the Identification of Minerals of Missouri's Lead Mines

The Eastern half of the state of Missouri is actually home to two different lead districts (also known as belts).  The French were mining lead from Missouri as early as the 1850's.  Famous mines like Mine LaMotte and Bonne Terre produced hundreds of tons of ore although very few specimens are seen from these mines today.  Galena was the primary ore, with copper, zinc and cobalt also present. These mines closed for good in the 1950's and have been flooded and inaccessible for over 45 years.  This early Mining District is known as the "Old Lead Belt". Geologists later theorized a similar type of deposit must lie on the other side of the St. Francis Mountains and discovered a new deeper area of mineralization primarily in Iron and Reynolds Counties, which become known as the "Viburnum Trend" (also New Lead Belt), and is the world’s largest galena deposit.  The mines of the Viburnum Trend have been prolific producers of chalcopyrite, pyrite, marcasite, and dolomite crystals.  The district has also produced by far the world's best siegenite and museum size and class galena, and calcite.  One of the first mines into production was the Indian Creek Mine, which was also the only major producer from Washington County.   This was also the northernmost mine in the district as development tended to move from the North to South.  The most characteristic mineral from Indian Creek was the galena. The crystals tended to be very smooth sharp and lustrous cubes with relatively large octahedral corners. This mine was also the first to close and specimens are very difficult to find today. Typical forms of galena from the Viburnum Trend are octahedrons almost always with small faces of the cube on the tips and cubes.  The octahedrons tend to be slightly dull and rough on the surface. The cubes often have small octahedral corners and a somewhat scaly surface almost unique to this district.  Either of the above criteria increases the likelihood of a specimen coming from the Trend. Galena was also found as tabular spinel twinned crystals from several of the mines (and is indicative of the Trend) although the most common and spectacular examples were from the Brushy Creek Mine.  Probably the most easily identified specimens from the district are the Marcasite/Pyrite on gray Calcite scalenohedrons from the Brushy Creek Mine.  These were first found in the early 1980's and then dealer Top Gem’s specimen collectors reworked the pocket in the late 1990's.  The second batch seemed to be a little less iridescent and rustier in color on the marcasite.  Almost all of the calcite found has been elongated on the c-axis.  The Sweetwater Mine has also produced many varieties of calcite, the most typical a long hexagonal crystal with a low angle rhombohedral termination.  No primarily rhombohedral calcite has been found in the Trend.  The best two indicators of a specimen from the Viburnum Trend are white to tan dolomite rhombs 1-4 mm in size and a dark gray dolomite matrix rock.  There is no chert found in the Viburnum trend.  Chalcopyrite crystals from the Trend typically have a rich brassy, sometimes iridescent, color and a high luster.  The crystals also tend to be modified or stepped unlike the sharp simple tetrahedrons of the Tri-State District.  Pyrite crystals larger than 1/4 inch are almost exclusive of the Trend. Marcasite often forms in botryoidal shapes with individual mounds up to 2 inches across.   Cobalt minerals are exclusive to the deposits on the Eastern half of the state.   Siegenite, linnaeite, and others have been reported from Mine LaMotte although not in large or noteworthy crystals.  The world's best siegenite crystals are found in the Viburnum Trend.  The Buick Mine was the first to report world-class specimens in the 1980's with sharp silver pseudo-octahedral crystals often twinned with other sulfides.   The largest siegenite crystals to come out of the Trend were mined in the early 1990's in the Sweetwater Mine with crystals over 1/4 inch in size.  The most common associated minerals with siegenite are marcasite and galena.  Replacement or casts of galena crystals with siegenite are highly sought after.  A spectacular find from the Brushy Creek Mine was made in the early 1990's with pyrite casts of galena crystals and siegenite crystals growing in dendritic form within the galena casts.

 

Add pyrite bars and gray drusy quartz on galena

 

After seeing one too many misidentified specimens from the Tri-State District and the Viburnum Trend across the Internet I have decided to see what I can do to help stop the spread of misinformation. The confusion starts with the fact that these deposits are both Mississippi Valley Type (MVT from here on out) in origin and produce world-class examples of calcite, galena, and sphalerite. Specimens of these including the associated minerals common to both deposits include; dolomite, chalcopyrite, pyrite, and marcasite are found in prominent museums and textbooks throughout the world. A lack of geographical knowledge of the state of Missouri is adds to the confusion. Even though part or all of both deposits are in the state of Missouri they lie over 150 miles apart. The purpose of the following information and pictures is to help those unfamiliar with the two deposits learn what to clues to look for to aid in proper identification of their specimens from the districts.

The Tri-State District was discovered first, near Granby, Missouri in the 1860's, so I will start with it. The name comes from the fact the District lies within three states hence Tri-State District. The States are Missouri, Oklahoma, and Kansas and tunnels underground used to run from one state to another. The early days saw hundreds to thousands of small mines right next to each other doting the landscape of Southwestern Missouri around the town of Joplin. As consolidation of the mines progressed primarily under the Picher Eagle consortium many of these small mines were connected underground to each other until eventually an underground network hundreds of miles long was created. It was possible to go underground in Kansas travel to Oklahoma, Missouri and back to Kansas without ever seeing the light of day. This had the effect of eliminating the specifics of giving a mine name to a particular specimen in the eyes of the miners as well as a number of collectors who went underground. They may have known what shaft they went down but once underground there was no telling what mine they were actually collecting in. Because of this many specimens get labeled Joplin, Missouri or Picher, Oklahoma that come from the district. When the specifics of a specimen are unknown to me I feel it is best to label the location as Tri-State District, Joplin, Missouri area. Most of the last collectors went underground with an old miner named Chink Enders who commonly used the old ore bucket of the Mid-Continent Mine in Treece, Kansas to lower them down into the labyrinth of passages. Chink knew his way around the confusing passages like the back of his hand and once underground I'm told he took off so fast in the old jeep he had down there no one would find there way back without him. By the early 1970's the mines were all closed and starting flood when Chink who was known to have a few enemies was found dead at the bottom of one of the shafts. By 1975 all the mines had flooded and no more specimens have come out from underground since. Specimens from the Tri-State District are pictured in almost every mineral related book I have seen. Huge calcite crystals nearly 2 feet tall and single galena crystals weighing several hundred pounds each have been found. The two best keys to identify specimens from the Tri-State District are the host rock and sphalerite crystals. Chert is the most common matrix

from the District and it's presence indicates a 99% chance it is from the Tri-State.

Chert is chemically SiO2 and most easily identified by it's hardness of around 7 (it will easily scratch glass/metal) and concoidal fracture. Sphalerite crystals are much, much more abundant from the Tri-State District and the presence of crystals larger than 1/8 or reddish in color are strong indicators is not from the Viburnum Trend. Sphalerite

Crystals larger than 1/4 inch are a sure sign the specimen is from the Tri-State

District. The next best keys to look for are pale pink classic saddle shaped dolomite crystals and sharp tetrahedral shaped chalcopyrite crystals larger than 1/8 inch. World class coxcomb marcasite crystals were found in the district although many have since disintegrated. Although marcasite in a coxcomb form is found in both location the presence of marcasite crystals larger than 1/4 inch is an indicator for the Tri-State district and crystals over 3/8 inch are almost a sure sign of a Tri-State District sample.

Calcite is common to both locations and should not be used as a primary indicator for either because of the wide variety of crystal form and similar colors. Exceptions are the famous large Stair-Step calcite which is only found in the Tri-State District are rare scalenohedrons with a purple tint believed to be due to inclusions micro marcasite crystals. Selenite and barite crystals are not common but have been found in the Tri-State District and not the Viburnum Trend. No fluorite has ever been verified from the Tri-State District and any specimen labeled that way is likely a Cave-In-Rock, Illinois specimen purchased by a collector when traveling through the Joplin area. Secondary minerals like pyromorphite and smithsonite are only found from the early near surface deposits of the district. Cerussite is a common white crust on weathered galena or rarely as small mostly microscopic crystals on galena.

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