Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Asian rubies come always with marble and salt

04.02.2004


Ruby deposits are the primary gem source in Central and South-East Asia. They are highly prized and have a special character: the rubies always occur as inclusions in marble. Geologists from the IRD and CRPG/CNRS (1) have investigated the tectonic and geochemical mechanisms involved in their formation and established a new model of how they generated. It involves feeder fluids resulting from solution of layers of salts present in the marble formations. These hot fluids were brought into circulation at the time of the Himalayan chain orogeny and provided the conditions for mobilization of the constituent elements of ruby and its crystallization within the marble. This genetic model gives the partner countries valuable information on the structure and geochemistry of ruby formations and tools necessary for improved targeting of prospection for this rare and highly sporadic type of mineral concentration.



Ruby is mineralogically the chromiferous variety of corundum gemstone, in other words an aluminium oxide in which some of the aluminium ions have been substituted by chromium. Chromium contributes, along with vanadium, another metal constituent of ruby, to the crystal’s red colour.

The most prized ruby deposits are those of Central and South-East Asia, like in the celebrated Mogok deposit in Myanmar (ex-Burma), from which the highest gem-quality rubies are extracted, reputed for their intense "pigeon blood" colour and their transparency.


In spite of their commercial interest, these deposits have attracted little geological research. However, they possess a special feature that have stimulated the interest of the IRD and CRPG/CNRS scientists for several years. The ruby crystals they hold are always present as inclusions in marble formations, which are calcareous rocks altered by high temperature. Research projects have been launched to determine in particular the origin of certain major constituents of the ruby which are usually absent from marbles--mainly aluminium, chromium and vanadium--, unravel the mechanisms of formation of these deposits, their age and their significance in the functioning of deep zones of the Earth’s crust. Combination of field data and results of laboratory geochemical analyses on samples taken from different deposits recorded from Afghanistan to Viet Nam, the team succeeded in establishing a new genetic model, valid for the whole of these deposits where ruby is associated with marble (2).

Ruby crystals form at high temperature, between 620 and 670°C. Dating of minerals contemporary with their growth, such as zircon and mica, performed in the different deposits gave the age of the ruby crystallization. Depending on the deposits, this was found to be 40 to 5 million years B.P., in the Cenozoic. The ruby is thus an excellent geological marker of the collision between the Indian and the Eurasian plates which set off the Himalayan uplift.

Analysis of liquid inclusions trapped by the rubies during crystallization revealed the participation of feeder fluids riches in salts and carbon dioxide, source of which has been defined by using their chemical composition. They result from the high-temperature solution of salts contained in evaporite-bearing beds (3) which are found in the impure marbles of Central and South-East Asia, rich in clays and organic matter. These fluids were subsequently set in motion under the influence of tectonic pressures linked to the collision of continental plates.

Their interaction with the marbles caused chemical reactions which freed aluminium and chromophor elements of the ruby, like le chromium or vanadium. These elements, initially held in only trace quantities in these rocks, were shown to be mobile in sufficient quantity to produce ruby in this geological setting. Dissolution of salts from the evaporite beds led within the marble to the creation of cavities in which very pure rubies, with well developed faces, were able to develop. Contrary to what theoretical models elaborated up to now would suggest, the proposed model shows the involvement of salts and mineralizing fluids of metamorphic origin, the mineralization of the rubies taking place in the heart of the marble formations.

This model, which is new for natural ruby, proves to be close to the molten salts method used in industry for aluminium production.

The presence of evaporites is therefore a key element for explaining these ruby mineralizations. It is a sign for the carrying rock of a primary environment of a particular nature, the "lagoon" type where sedimentation took place in close relation with the ocean.

Their existence inside the marble formations is still, moreover, rare, which fits the very small number of deposits recorded and their small geographical spread. For the partner countries that are mining these deposits, this model brings information about the history, the structure and the geochemistry of these ruby formations, knowledge which is essential for conducting new prospecting campaigns in these regions of Asia.

Bénédicte ROBERT | EurekAlert!
Further information:
http://www.ird.fr/

More articles from Earth Sciences:

nachricht Mineral discoveries in the Galapagos Islands pose a puzzle as to their formation and origin
19.10.2018 | Johannes Gutenberg-Universität Mainz

nachricht Massive organism is crashing on our watch
18.10.2018 | S.J. & Jessie E. Quinney College of Natural Resources, Utah State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Goodbye, silicon? On the way to new electronic materials with metal-organic networks

Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.

Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Conference to pave the way for new therapies

17.10.2018 | Event News

Berlin5GWeek: Private industrial networks and temporary 5G connectivity islands

16.10.2018 | Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

 
Latest News

Nanocages in the lab and in the computer: how DNA-based dendrimers transport nanoparticles

19.10.2018 | Life Sciences

Thin films from Braunschweig on the way to Mercury

19.10.2018 | Physics and Astronomy

App-App-Hooray! - Innovative Kits for AR Applications

19.10.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>