We are in an area of Palaeozoic limestone and dolomite in western Canada.
In these pictures the limestone appears to be disturbed and a rounded "blob" has been introduced (?). It is extremely hard (estimate more than 7 in Mohs scale).
The "blobs" have a thin white reaction rim and appears to have "grown" in place (much like garnets grow during metamorphism).
I will appreciate any explanation that you might have.
Dear Mr. Issigonis,
it is a mixture of calcareous rocks, starting off from simple flasered limestones (dark flasers are made up of siliceous material, which can be derived from pressure solutions along stylolites to tuffaceous intercalations. All of these kinds of non-calcareous intercalations are known from Late Devonian limestones of the Central European Variscan orogens). Ball structures point to load casts which evolved at the contact of siliceous and calcareous muds which moreover underwent slumping along submarine swells (synorogenic flysch sediments). It is important to get an insight into the composition of the dark flasers (phyllosilicates?). The dark rounded clast is alien to this facies and extrinsically introduced. As it is not in equilibrium with the remaining calcareous surrounding matrix a reaction rim came into existence.
Kind regards
H.G.Dill
Dear Michael, it looks like a silicified limestone. I have seen similar textures at a gold prospect in PNG. Limestones are quite permeable for hydrothermal fluids and, hence, even strong silicification can form these patchy textures.
Dear Michael Issigonis, its maybe limestone and itts one curing of the Drilling and the main Reason of is the another materials that join with limestone
Michael,
i would agree with Harald that the clast in question has been introduced from outside. If it was a chert nodule, I would expect some effect on the surrounding carbonates, but it looks as if the carbonates are deposited against it. It is likely that it is a quartz fragment, but wonder if it is a garnet in that the shape suggests a subhedral garnet crystal.
George
Dear George J. Strachan i am also agree with you but it will be out side materials
Hi，
I support the view of chert nodule or siliceous block. I have seen similar structure in the distribution area of ELIP volcanic rocks in China. It is indeed siliceous block in carbonate rock, similar to nodule. I suggest further study in combination with thin sections.
Best,
Liu
With that form and a hardness of over 7 you must be dealing with chert nodules. Their shape is not unlike many chert nodules I have seen in Lower Carboniferous & Jurassic limestones. There may be some metamorphic overprint creating the rims but I cannot see any details.
Dear @ Peter Strogen Liu Chenming Hafizullah Rasouli George J. Strachan Daniel Müller Mohsen Ehteshami-Moinabadi and Harald Dill,
Thank you all for your important input to identify the siliceous "intruder" into the limestone of western Canada and your suggestions for further work.
The black colour is due to silica impurity. Such black siliceous limestones with nodular cherty carbonate are ubiquitous in Palaeo-Mesoproterozoic- Cuddapah Basin of southern India. The rounded blob appears to be a black chert nodule. (???).
Dear Ramesh Chandra Phani
After reading all the contributions from the respected researchers above I also come to the conclusion that these blobs are chert nodules.
Nice to know you have similar formations in southern India, but of much older age.
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