Skarns:
Michelle has also given a similar definition
techstocks.com
Limestones and dolomites are sedimentary but when they become skarns they are metamorphic, the calcite and dolomite minerals are recrystalised under the action of heat and mineral water, the magmatic intrusion can also form veins or pipes of igneous rock. So we have the three types of rocks present in the formation.
The three types of rocks evolve in a perpetual cycle under the influence of erosion, sediment deposits, heat and pressure, fusion...k At the end of the cycle a rock of sedimentary origin may become igneous if it is melted in a magma.
The mineral CaCO3 is calcite (calcium carbonate). Isn't the formula for dolomite CaMg(CO3)2?
Carbon dioxide from the air disolves in water to form carbonic acid (H2CO3), or hydrogene ions H+1 and bicarbonate ions (HCO3)-1 in solution. In the right conditions of temperature, pressure and concentration, metallic ions will combine with the bicarbonate ions to form carbonate, salts and carbonic acid. That why skarns deposits can present some sort of metal mineralization.
The basic reaction in geomorphology:
{CaCO3 (calcite) + (H + HCO3)<-[H2O (water)+ CO2 (carbon dioxide)]}
=> Ca(HCO3)2 (Calcium Bicarbonate)
Carbonates can be of a great variety (about 70) of minerals depending on the elements present at the time of formation. Calcite and dolomite are the most common. Skarns can also be silicates such as pyroxens, diopside (magnesium), johannsenite (magnesium and iron), hedenbergite (iron), augite (aluminium, iron, titanium), wollastonite.
While working on this definition, I have just found a great site for those who want to know all there is to know about skarns. The work is all done!
wsu.edu:8080/~meinert/skarnHP.html
This is also a nice site about wollastonite skarns, I found a few months ago.
nereus.geology.ubc.ca
That doesn't solve our problem. What we are trying to do is to translate the word "manto" or to find the closest equivalent. The formation seems like a variation of a skarn type formation. Is a manto the vein or the rock itself?
How would you explain a skarn in French... or in Spanish? It overlaps categories in most classifications. Some of the skarn are classified as carbonates, others as silicates.
Thanks for helping put some pieces in the puzzle, Francois! |
