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Hey Tariq,
Recently we had a field visit to the Sona Pass area near Karachi,there is a ridge-like feature there by the name of Pir Mangho Limestone, on the foothills of the ridge, there were fractures and the gaps in between had been filled(we put some acid on the filling and found that it was limnestone), my question is that how many types(common) of fillings and why are those gaps in between fractures filled? Thank You.

Answer
Dear Hasan,

Thanks for sending me your question.

naturally occurring rocks are subjected to stresses which produced fractures of varying magnitude and dimensions. Fault is a large fracture plane varying in size and area from few yards to several tens and to hundred of miles whereas fractures or joints are smaller units covering micro inches to several inches.

The fractures have usually been filled when the liguid fluids flow through them and settled down due to any reason, i.e., cooling or pressure drop etc.. These fluids are being generated by various natural processes. Hydrothermal processes (carrying hot water originated  from deeper source)are main source of these fractures filling material.

The chemistry of fluids is primarily depend upon the nature of source and its migrating pathways. For example, water flowing through basalt will be  silica rich which will eventually deposit quarts (SiO2)in fractures.

Similarly, limestone fractures are usually filled with calcite (Ca CO3) or chlorite (ClO2) but there are wide range of other minerals which partially associated with calcite filled minerals.

The most common fractures filling material are Calcite (The calcite is a pure CaCO with low contents of FeO, MgO and MnO, in most calcite the total amounts of trace components are < 1%)

Chlorite/corrensite (Chlorite and corrensite are the most important Fe2+ bearing fracture mineral . The FeO content in chlorite/corrensite is normally between 20 and 0% and the MgO content varies between  and 2%. The CaO content is normally between 0.2 and 0.9% due to the
corrensite component, Laumontite (Laumontite has a CaO content between 10 and 1% and FeO content below 0.%),

Hematite, Quartz, Adularia, Prehnite, Pyrite, Epidote (Epidote has a Fe2O content between 9 and 1% and a MnO content between 0.1 and 0.8%,the CaO content is c 2%)

Clay minerals (Biotite, Goethite, Asphaltite (Asphaltite consists of a mixture of hydrocarbons and is often associated with sulphides)).

Not necessarily all fracture in nature are filled but rather there have bee open fractures without filling as well.


Hopefully, this answer will be helpful.

Please do not forget to RATE this answer.

Regards

Tariq

References:

Mineralogy and geochemistry of rocks and fracture fillings from Forsmark and Oskarshamn: Compilation of data for SR-Can. Henrik Drake, Björn Sandström Isochron GeoConsulting HB Eva-Lena Tullborg, Terralogica AB November 2006

Forsmark site investigation 40 Ar/ 39 Ar (adularia) and Rb-Sr (adularia, prehnite, calcite) ages of fracture minerals. Björn Sandström, Earth Sciences Centre, Göteborg University Laurence Page, Department of Geology, Lund University Eva-Lena Tullborg, Terralogica AB, Gråbo
October 2006  

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Syed Tariq Hasany

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MY HUMBLE REQUEST. BEFORE SENDING A QUESTION PLEASE READ THE FOLLOWING CAREFULY. ANSWERING ONLY PUBLIC QUESTIONS. Ask questions of exploration of Petroleum, and specific regions for specific answers about Pakistan, Central Asia, Middle East and Far East. Ask questions of Business side of the petroleum Geology. Love to guide students and also Career related issues PRIVATE QUESTIONS on thasany@yahoo.com I am not expert of Hard rocks (Igneous and metamorphic rocks)Volcanic activity and related petrology, mineralogy and its exploration. BE SPECIFOC WHAT YOU WANT TO KNOW AND ASK WITH DIGNITY AND RESPECT. Show me your determination and commitment to learn. PLEASE TRY TO WRITE RIGHT, PROPER AND CORRECT LANGUAGE. DO NOT USE TEXT(SMS)STYLE. Thanks TARIQ

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