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Hi. I've been watching a new BBC documentary on colour. They claimed that all the gold we have found on Earth came here in meteorites - that there was gold in the dust that the planet was originally formed from, but that none of this is on the surface, because it's too heavy. This put two questions in my mind:

1. Is the same thing true of the iron that's available in mines? Has it got here in meteorites, too? With all the original iron in the molten core of the planet? Or alternatively is iron light enough to surge up from the depths of the planet via volcanic activity?

2. Do we know where the original gold is? Is it mixed up in the molten iron core in the centre of the earth? Or is there a sphere of gold in the middle? Would our instruments be sensitive enough to identify something like that?

Hope you can help. Thanks for reading this anyway.

Rollo

Answer
All iron deposits that you see are in face do not have iron as element but are huge deposits of common iron minerals hematite and magnetite  and to some extent of goethite.

These minerals are formed mainly by direct magmatic activity and also due to volcano sedimentary processes in sea and oceans. In both cases the iron combines with oxygen during the process of crystallisation or precipitation - a geochemical process. To my knowledge, this elemental iron is nor derived from the core, but, is in fact re-circulated material that forms the mantle and crust of the earth. There is no scope of any surge of iron from the core to surface of earth.

Same holds good for gold, the crustal and mantle rocks have gold in amounts less than the detection limits of common laboratory analysis but, the re-circulation of material of crust and mantle locally form rocks rich in gold - geochemical processes we understand little at present.
I cannot say if all gold on earth came from meteorites.

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N.K.Agarwal

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Would be happy to answer : General Geology, Engineering Geology, Economic Geology, Geomorphology, Geoenvironment, Tectonics, Natural Resources inclusive of Rocks & Minerals, Exploration, Science Policy etc.

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Geological-Geotechnical Solutions and professional advice. I have over 34 years of professional experience of working as a geologist in diverse mountainous terrain. I have professional skills for planning. programming, executing and monitoring of : (1) Engineering Geological investigations in Hydropower and Developmental projects, (2) Landslide and Disaster Management etc. (3) Natural Resource Management and Programming (4) Geological Mapping (5) Geoenvironmental Management (6) Mineral Exploration (7) Water Resources Management, (8) Integrated Watershed Management, (9) Training on - Natural Resource Management, Geoenvironmental Management, Waste Management, Geohazards, Geotechnical Investigations, Data acquisition & interpretations, (10) R&D Initiatives and Societal issues etc.

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M.Tech.(Applied Geology), University of Roorkee (now IIT Roorkee).

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Worked in the Geological Survey of India for aabout 32 years. Presently - GeoConsultant & Advisor - HIGEOS India

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