Silberbrünnle Mine, Haigerach, Gengenbach

General

The Silberbrünnle (Silver Spring) mine is situated in the upper Haigerach valley, about 2 km north of Haigerach and 6 km north of the inner city of Gengenbach. Haigerach can be reached from Gengenbach on a small road. From federal road B 33 you take one of the two exits to Gengenbach, then take the road towards the inner city (Innenstadt). Shortly before you come to the old watchtower at the southernmost point of the old city wall,  the road crosses the railroad tracks. Here you take the turn to the left, following the main road (road sign to Offenburg and Ohlsbach). The road follows the city wall a quarter of a circle. Then there is a oneway road branching off to the right with a road sign to Haigerach. Turn right and drive to Haigerach. In Haigerach stay on the main road following the creek. After leaving the village, the road goes further to the north until it ends in a parking lot (at the right side). The main road is becoming a forest road then. You are not allowed to drive up further. From the parking lot take a hike of one km, until the forest road leaves the creek in a big curve to the right. Here you have to take the smaller road that follows the creek further up, called Diebsweg. Following the road about 200 m, you will recognize the open stockpile at the right bench of the creek. At the dump and in a small collector's dig/trench on a quartz vein with galena 150 m horth of the stockpile there are very limited collecting possibilities. The stockpile is worked over and over by at least three generations of collectors. Even quartz and pseudomalachite, the most common species at the stockpiles, can only be found in small pieces todays. Collecting possibilities todays are pretty much limited to micromounts.

Geology

In the Haigerach valley crystalline basement rocks (Gneisses and Rhyolites) are predominant, partially Bunter Sandstones are covering those.

The Gneisses (Central Black Forest Gneiss Complex) do have proterozoic precursors, metamorphosis took place at 600 and 325 Ma. The second metamorphic event, the hercynean orogenesis, led to a high-temperature overprint. Different precursors led to different types of gneisses. Leptinites, mixed gneisses and metapelites are the most common types. Metamorphism reached 750-900 °C in this area.

In the Haigerach valley, especially in the area of interest, paragenic gneisses are predominant. Lenses of amphibolites and calcsilicate rocks can be observed, but are of no importance as hostrocks of the veins.  Directly to the northwest of the mine, permean, late orogenic rhyolite with well preserved fluidal textures can be found outcropping. The porphyries do cover the gneisses nappe-like. At higher elevations relicts of the mesozoic cover can be found. In the upper Haigerach valley coarse-grained lower triassic sandstones (Bunter Sandstones) are the only type of sedimentary cover rocks. All of the higher strata are eroded in the tertiary due to uplift of the Black Forest Shield and erosion in the valleys.

Another consequence of the tertiary uplift and the formation of the Upper Rhine Graben are NW-SE striking fault zones almost perpendicular to the Rhine Graben fault zones. Those can be found in the lower Kinzig valley even at a topographical scale. The lower Kinzig valley from Offenburg to Wolfach is following such a fault zone, the so-called Kinzigtal graben.  

The Silberbrünnle vein is part of a thrust zone (10 cm height difference), extending from Ohlsbach to Schapbach.

It is questionable if the Silberbrünnle vein is an old hercynean vein system reactivated in the tertiary, or a tertiary mineralization, following the new fault zone.

Mining

Most of the data on mining activities in the upper Haigerach valley are lost.

The first mining activities in the area are yet unknown. SAUER in 1894 (according to BLIEDTNER and MARTIN, 1986) said the earliest mining activities to have taken place in the first period of mining in the Duchy of Baden (12 th/13 th century). Those old mining activities wouldn't be recognizable in the areas due to forestal activities. The Imperial Government in Innsbruck (Austria)took inquieries on this mining in 1515 and 1518.

According to GOTTSCHALK, 1995 the height and width of the adit are relatively big as to a hand-chisseled mine. This is in the contrary to most of the medieval mines. Acoording to FAUTZ, 1972 (in BLIEDTNER and MARTIN, 1986), in 1520 a mining company from Strassburg got letters of liberation and a mining order (regulation) for the Haigerach mine. In 1529 the monastry of Gengenbach demanded the tenth part of all incomes from mining. According to Gottschalk, 1995 the tenth could have been demanded in case of expected earnings and cannot be seen as a sign of actual mining.  

The last period of mining took place at the beginning of 20th century. In 1902 Mr. RINGWALD claimed the mine (called Haigerach mine then) on manganese ores. which were solely of interest in this period. In 1903 a draft of the adits was drawn.  It is shown in both BLIEDTNER and MARTIN, 1986 and GOTTSCHALK, 1995. In 1909 the mine was abandoned. No ore mining and extension of the mine were done in this period. In 1925 the mine finally got out of any claiming

If and when any ore mining took place at Silberbrünnle mine is subject matter to controversial discussions.  To the north of the stockpile a little smelter is located. In the surrounding area even today slags, relicts of charcoal and shards of ceramics can be found. Another characteristic material in that area is reddish to pinkish white, heat-treated quartz, which is poor in copper ores but rich in lead ores. Lead minerals such as minium are direct results of heat treatment.

Parts of the slags are rich in copper minerals, often small blobs or pearls of copper do occur. This can be seen as a proof of assay experiments.

According to GOTTSCHALK, 1995 the material of the stockpile maybe is filling an old opencut on galena-bearing quartz-veins parallel to the copper-bearing main vein, which are not outcropping in the adit. The poor ores in the adit are not supporting extensive mining in the area. Only pseudomalachite, malachite and chalkopyrite as Cu ores and goethite as a Fe ore coming in question as ore minerals. No cavities due to ore mining can be seen in the adit. For a pure exploration digging the size of the adit/galleries and the stockpiles are extremely oversized. The port of the adit is filled in and cannot be located in the countryside. A shaft, which had been open in the end of 20th century, is filled in with tree roots and branches and therefore inaccessible.

Mineralization

The Silberbrünnle vein group (actually it's a group of veins with parallel striking directions and one main vein) comprises quartz veins (often with chert-like 1st generation quartz and intense brecciation). Quartz always is present as the main constituent of the veins. Pseudomorphs after baryte can occur. There is no primary fluorite and baryte, in the contrary to almost all of the Black Forest veins. This could maybe seen as a tertiary overprint of an older mineralization. Some of the veins at Nordrach (to the the east of the Silberbrünnle mine) are of the same striking direction and consisting of baryte with siderite and/or hematite.  Maybe at deeper levels primary mineralization types with siderite and chalkopyrite ores in baryte do occur. Manganese oxide-hematite masses in the quartz vein infill and limonite pseudomorphs after siderite xls seem to support the idea of primarily siderite-bearing veins.

Mineral Paragenesis

 Attention! This description is based on observations from stockpile material and preliminary. It is supposed to help a collector identifying the minerals. 

Mineral Paragenesis at the stockpiles 

1a) Quartz-copper-Paragenesis
mainly coarse-grained white, s´more rarely agate to chert-like quartz with grains of copper sulphides (mainly chalkopyrite, often with rims of digenite or chalcocite, minor djurleite, luzonite and tennantite) and their secondaries (malachite, pseudomalachite, agardite, brochantite, minor azurite and tenorite) as well as limonite, goethite and Cu-Fe arsenates such as olivenite and bariopharmacosiderite. Main paragenesis at the stockpiles.

1b) Quartz-copper-Paragenesis with mit Cu-Pb-Fe minerals

Much like a) but lead-bearing minerals are more frequent. Galena as a primary source of lead usually is not visible, as well as pure/rich lead secondaries such as cerussite or pyromorphite. In addition to the minerals of paragenesis type a) you can find beudantite/segnitite, duftite, carminite, bayldonite and gartrellite/mawbyite.

2. Bismuth-(Copper) Paragenesis
In a white to greyish, light coloured quartz, often with pseudomorphs after  baryte , besides chalkopyrite, emplectite can be identified as ore mineral. Usually secondary Bi minerals with predominant bismutite (often pseudomporphs after emplectite needles) and minor mixite, beyerite, eulytine and bismutoferrite can be seen at the specimens. 

3. Fe-Mn Paragenesis
Pinkish to reddish brown (hematite) or greyish black (manganese hydroxide) as well as limonitic masses. Kolloidal or botryoidal structures with banded textures are common. Those are low-temperature to secondary minerals, possibly alteration products of siderite.  Those manganese ores, which can only be found in some enclosed parts of the vein, had been the aim of the last exploration activities in 1909. Amongst the minerals present are hematite, pyrolusite, cryptomelane, ramsdellite, limonite and hausmannite.

II. Paragenesis present both at the dump and in parallel veins

4. Lead-Chert-(Copper) Paragenesis

A grey to greyish blue (due to sulphide inclusions) to yellowish grey chert-like quartz is the host of galena and chalkopyrite. In a parallel vein outcropping 150 m to the nort of the stockpiles, small fahlore-like inclusions of schapbachite can be found very rarely. Actually, this is the first occurrence of cubic AgBiS2 as a mineral (i.e. formed by natural processes) at room temperature. The original schapbachite from Schapbach (30 km to the east of this mine site) in fact is matildite. Chalkopyrite grains ovten are rimmed by blue-metallic covellite. Galena usually is far more weathered. Cerussite, anglesite, sulphur, bindheimite (oxyplumboroméite most likely according to the new IMA nomenclature), pyromorphite and mimetite are formed from weathering galena. Wulfenite and linarite are far less common, the first being rather rare.  Cu secondaries are present, too, but Pb is predominant. Malachite and duftite are amongst those.

III. "Artificial Paragenesis"

The paragenesis types listed here are due to human influence.

5. "Fire paragenesis"
There are certain associations of secondary Pb-Cu minerals that can be seen as an indication of heat treatment of vein material.

 In addition to a very distinct type of brittle, easily to break, reddish to pinkish to pinkish white quartz Pb-Cu sulphates/carbonates and carbonate-sulphates such as elyite, caledonite, leadhillite/susannite  and hydrocerussite as well as lead oxides (minium, litharge, massicotite) are indications of this type. There is a description fro Silberbrünnle mine by GOTTSCHALK, 1994. 

The term "fire paragenesis" is of better use than the original term "fire setting paragenesis" as there is no proof of the utilization of the medieval method of setting fire to hard quartz veins to weaken them at the Silberbrünnle mine. Probably the rocks had been heat-treated by smelter experiments.

6. Slag Minerals

Slag minerals and the place of smelter experiments are described by GOTTSCHALK et.al. in 1995.  The slag locality is situated 150 km north of the stockpiles in close proximity to a very small creek. Three different kinds of slags are described in the said article. Only one is of interest to collectors: Copper-rich slag. The violet-brown matrix with small vesicles has often pearls of fresh copper. Green to blue secondaries are often present in the vesicles. Findings have become extraordinarily rare. Copper minerals present are copper, copper sulphides (chalcocite, covellite), chalkophyllite, brochantite, langite, malachite and rarely schulenbergite.

In addition to those common and distinct paragenesis types, there is some kind of a sulphate paragenesis with extraordinarily rare species one could call the haigerachite paragenesis. As far as I know only one finding has been made so far.

Quartz with pyrite is the matrix. Haigerachite (+ a possibly third new mineral, a hydronium-rich type of haigerachite), gengenbachite, diadochite and gypsum are the sulphates present.

Mineral List

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