ABSTRACT

The formation of large, economic borate deposits requires a boron-rich source, the means of transporting and concentrating the boron in a restricted environment, and mechanisms for the preservation of the deposit. There are several Miocene basins in western Turkey containing world-class borate reserves, with mineralization present as stratabound deposits in volcano-sedimentary successions. Although it is well-documented that the conditions required to form and preserve large borate deposits are most common in post-collisional tectonic settings (of which western Anatolia is a prime example), recent advances in the understanding of extensional tectonics and volcanism in this region, make it possible to gain fresh insights into their formation. Here, we suggest that formation of one of the largest borate deposits in the world was intimately related to the recently recognized Kırka-Phrigian caldera that lies in the northernmost part of the Miocene Eskişehir–Afyon volcanic field. Following caldera collapse, the basin filled with lacustrine sediments and volcaniclastic deposits with the boron mineralization concentrated in two main sub-basins: Sarıkaya and Göcenoluk. The close spatial and temporal relationship between borate deposition and the vast Early Miocene ignimbrite deposits that surround the caldera (and contain high levels of elements associated with mineralization) strongly suggest that the ignimbrites were the major source of boron. The boron was transported by geothermal fluids and post-volcanic gases that vented into warm water at the base of the caldera-paleolake system and was then concentrated during cycles of sedimentation and evaporation, with most of the mineralization concentrated along a N-S striking fault system.

摘要

大型经济型硼酸盐矿床的形成需要富硼资源、在受限环境中运输和浓缩硼的手段以及矿床保存机制。土耳其西部有几个中新世盆地，其中包含世界一流的硼酸盐储量，矿化以火山沉积序列中的层状沉积物形式存在。尽管有充分证据表明形成和保存大型硼酸盐矿床所需的条件在后碰撞构造环境中最为常见（安纳托利亚西部就是一个典型的例子），但对该地区伸展构造和火山作用的理解的最新进展，使其有可能获得对其形成的新见解。这里，我们认为，世界上最大的硼酸盐矿床之一的形成与最近确认的位于中新世 Eskişehir-Afyon 火山区最北端的 Kırka-Phrigian 火山口密切相关。火山口坍塌后，盆地充满了湖相沉积物和火山碎屑沉积物，硼矿化集中在两个主要子盆地：Sarıkaya 和 Göcenoluk。硼酸盐沉积与火山口周围大量早中新世熔凝灰岩沉积物（并含有大量与矿化相关的元素）之间密切​​的空间和时间关系强烈表明，凝灰岩是硼的主要来源。