South Sea dive trip successful

Interview on underwater storage research

Research diving boat Pisces V © GPI Kiel / BGR
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During their dive trip from 3 June to 3 July 2005, an international research team investigated a chain of submarine volcanoes in the Tonga deep-sea trench. The expedition took place under the direction of the University of Kiel and the Federal Institute for Geosciences and Natural Resources in Hanover. Ulrich Schwarz-Schampera reports on first results in an interview.

Would you rate the dive trip as a success?

Black Schampera:

The results even exceeded our expectations. Thus, we have located two volcanoes of highly active hydrothermalism and investigated. A highlight was certainly the discovery and sampling of the shallowest known high-temperature hydrothermal field in the world in a water depth of only 385 meters. Here we were able to observe the process of phase separation, that is, the "boiling" of the mineralizing solutions and the separation of a gas-rich phase. This process is central to the gold enrichment in these systems. Analyzes will show how these processes have influenced the deposition of gold.

So gold in the South Sea? Is there any thought of mining these raw materials?

Black Schampera:

According to current knowledge, which is almost exclusively 2-dimensional and provides no information on the depth extent, potential occurrences are rather small compared to land-based deposits. However, they can have considerable gold enrichment. In fact, one of the largest international mining companies in the gold mining industry is exploring active hydrothermal fields off the coast of Papua New Guinea. Nevertheless, economic reduction seems unlikely at present.
With a gripper arm, scientists of the submersible PISCES examine the sulphide plates on the seafloor. © GPI Kiel / BGR

What scientific purpose did you pursue with this dive trip? display

Black Schampera:

The expedition and the subsequent investigations serve the basic research and the understanding of storage-building processes. Many large gold deposits occur in the area of ​​archipelagos and magmatic arcs such as Papua New Guinea, Indonesia, Phillippines or South America. What they all have in common is that they are bound to volcanic activity. In submarine island bundles with comparatively shallow water depths of less than 1, 000 meters, such gold-bearing hydrothermal deposits have only been known for some time. Their investigation allows conclusions to be drawn on active storage-building processes from the origin of metals through their transport to deposition.

Why are the deposits bound to volcanism?

Black Schampera:

Plate tectonics as well as petrogenetic, ie rock-forming, processes play a central role. The formation of gold and nonferrous metal enrichments takes place in hydrothermal fields in the area of ​​island arc systems above subduction zones. In these zones, the overlying sediment and a small portion of the oceanic plate are melted and form magmatic melts. Here are also fluidmobil designated elements supplied, which include metals such as copper and gold, but typically include arsenic, antimony and mercury. Volcanic magma chambers also serve as a heat engine for the circulation of mineralizing solutions.

And how is it then to enrich these metals on the seabed?

Black Schampera:

This depends very crucially on factors such as the sulfur concentration and the degree of oxidation of the melt. If the sulfur content is low and the melt is oxidized, the metals accumulate in the fluid (volatile) phase during magma evolution and may be released as a result of volcanic eruptions and mineralizing processes. In addition, metals from the igneous rocks are released by hydrothermal circulation of altered seawater and in turn contribute to the enrichment of dissolved metals. The metals released from the magma and the dissolved elements from the magmatic adjacent rock frequently reach the area of ​​the seafloor together, where they are precipitated by cooling in the form of sulphides.

Are all the riddles solved by hydrothermal fields and the formation of deposits?
This active hydrothermal vent lies at a depth of 385 meters and is ten meters high. At its upper end, a hydrothermal solution with a temperature of 245 C emerges. The chimney (= chimney) has a barite structure (= barium sulfate BaSO4) and a core of pyrite and sphalerite (FeS2 and ZnS). GPI Kiel / BGR

Black Schampera:

Unfortunately no, because our knowledge of the submarine hydrothermal fields is far too selective and locally limited. For example, oceanic archipelagic and backward systems with a length of more than 100, 000 kilometers are difficult to comprehensively explore. However, our investigations have shown that the development of hydrothermal fields and the formation of reservoirs is influenced by a large number of different parameters such as water depth, temperature, chemical composition of rocks and fluids, as well as spreading processes and volcanic eruptions. Nevertheless, there is still plenty to do. So next, we mainly strive to investigate the depth extension through drilling.

Have you discovered any other special features during the dive trip?

Black Schampera:

Surprisingly, we were surprised by the enormous extent of the arched islands off Tonga, which in some cases clearly exceeds the size of volcanoes on land. Diving into over 1, 000 meters deep volcanic craters with powerful volcanic lava flows and deposits has a great fascination. The abundance of wildlife, including sharks, stingrays and fish, anemones, corals, bizarre colonies of unicellular organisms, and bacterial mats that are extremely widespread, is remarkable. Here, the occurrence of a specific hydrothermal fauna of mussels, crabs, crabs and bacteria is of particular importance.

Link: Gold in the South Seas?

(BGR, 12.07.2005 - AHE)