Glendasan is for Galena - DP/EC71 EarthCache

The lesson associated in this EarthCache is to let the reader and visitor learn more about mining in Wicklow County in particular the Old Hero mineral processing site.

How to claim this EC:
This cache takes you on a very short trip from car park to GZ coordinates. At these coordinates there is a distinct quartz vein (noticed a "tear" in the smoothish granite surface. The questions and tasks all relate to this vein.

1. What is the orientation of this quartz vein? A- North-South; B- E-W; C- NW-SE and D- NE-SW (please choose one)
2. What is the average width of this vein? A- 0.30m; B- 1.0m; C- 0.05m; D- 0.14m; and E- 0.23 m (Please choose one).
3. Is the vein filled in with white, transparent quartz crystals? A- Yes; B- No (Please choose one)
4. At the apex of the granite boulder, how wide is the vein? A- 0.12m; B- 0.07 m; C- 0.5m; D- 0.87m; and E- 0.23m (Please choose one)
5. Knowing that galena is a silvery metallic mineral, do you see any within the vein? A- Yes; B- No (Please choose one)

Please send the answers to these tasks to leinadoligc@gmail.com . If they’re correct, your log will stand and you won’t hear from me, otherwise be sure that you will contacted.

Galena

Galena (PbS), is the natural mineral form of lead(II) sulfide. It is the most important ore of lead and an important source of silverGalena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms. It is often associated with the minerals sphalerite, calcite and fluorite. (Source: Here)

Lead is a bluish-white soft metal that turns a dull grey when exposed to the air. As a metal, it is highly resistant to corrosion. This is why lead has so many applications in both modern and historical times. Today lead is widely used in the construction of buildings, weaponry, electronics assembly and even for shielding against radiation. Lead has been used for thousands of years because it is widespread and easy to extract and work with. (Source: Here)

Glendasan - brief history

Mining in this area dates back to the 1790s when the manager of the Avoca mines, Thomas Weaver was commissioned by the Government to undertake a survey of gold in County Wicklow. Not long after the 1798 Rebellion he discovered a rich vein of lead ore in the Glendasan valley.  In 1809 Thomas Weaver set up the Glendalough Mining Company in partnership with local investors. A more detailed history can be obtained in the Glendalough Mining Heritage Project.

Geological setting at Glendasan

The Caledonides of southeast Ireland comprise a thick and varied Lower Palaeozoic succession of marine turbidites ad shales, with volumetrically important Ordovician volcanic rocks, that have undergone polyphase deformation and low grade regional metamorphism. The Leinster Granite batholith, comprising 5 contiguous, concordant and largely contemporaneous plutons, was synkinematically emplaced into the Lower Palaeozoic succession at approximately 405Ma, coincident with the last major Caledonian deformation event in the region.

Mineralization occurs in the qurtz veins that follow the line of faults or previously emplaced pegmatite/aplite veins. Their strike direction varies but most are orientated at a high angle to the Leinster Granite margin. Yhe longest vein, the Luganore Lode, was worked over a length of almost 3.5 km and is typically < 6m in thickness. In kost instances, brecciation preceded and followed deposition of sulphides.

The mineralized veins are largely confined to the granite but a few cross the granite/wallrock contact where particularly rich mineralisation has been found. The mineralogy of the veins inludes major galena (PbS) and sphalerite (ZnS), subordinate chalcopyrite (CuFeS2) and pyrite (FeS2) and minor amounts of haematite (Fe2O3), tetrahedrite ([Cu, Fe, Ag, Zn]12Sb4S13), native silver (Ag), pyrargyrite (Ag3AsS3), covellite (CuS), rammelsbergite (NiAsS2), jamsonite (Pb4FeSb6S14), cassiterite (SnO2) and scheelite (CaWO4). The gangue consists of quartz (SiO2), barite (BaSO4), calcite (CaCO3) and fluorite (CaF2).

Of interest:

If you're interested in learning a lot more about the history of this area, see the download material Exploring the Mining Heritage of Wicklow County.

Source material
Minerals4EU - Field visit to Avoca and Glendasan,, Co. Wicklow. 2014, Geological Survey of Ireland, 16p (Unpublished)

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