Bubble mineralization is a process by which mineral particles are concentrated in cavities created by the escape of dissolved minerals from shallow pockets of water into the surrounding, permeable rock matrix. This process is particularly important in the precipitation of zinc, iron, and other metal sulfides within cavities of ore-bearing veins. It is a common feature of many important ore deposits, including sedimentary-exhalative (SEDEX) or Mississippi Valley-type (MVT) deposits, as well as most orogenic gold deposits, such as those associated with Mesozoic-Cenozoic accretionary belts in the Circum-Pacific region. Bubble mineralization is a key process in the ore formation process by which ore minerals, particularly sulfide minerals, are concentrated from their immediate host rocks.
The process of bubble mineralization is associated with the partial dissolving of previously deposited ore-bearing mineralization. This cause a variety of mechanisms, such as low pH, reducing conditions generated by nearby igneous intrusions, and oxidative processes initiated by rising and falling groundwater. In all cases, soluble ions are released, followed by the concentration and precipitation of metals in cavities created by the evaporated mineralization or hydrothermal solution. This process is often observed in major ore deposits like those of exhalative-sedimentary and Mississippi Valley-type. Bubble mineralization, however, can occur at a variety of scales, from microscopic to large scale regional metalliferous deposits.
The processes associated with bubble mineralization form part of a cycle of mineral dissolution and precipitation. In local ore deposits, bubble mineralization facilitates the formation of pockets of sulfide minerals within rock matrixes. These pockets are then further concentrated and surrounded by minerals such as calcite, quartz, pyrite, siderite, and barite. As the mineralization continues, these ‘bubbles’ become evermore concentrated until their contents are almost pure concentrations of sulfide minerals.
While bubble mineralization is a well-recognised process in ore deposits, it is often difficult to distinguish from other ore formation processes such as sedimentary exhalation and hydrothermal replacement. These processes are described in detail in many ore deposit models. However, certain characteristics can help distinguish bubble mineralization from sedimentary exhalation. For example, bubble mineralization is often accompanied by re-mineralization of the original ore-bearing mineralization, whereas sedimentary exhalation produces a much more uniform deposit of sedimentary ore. Furthermore, bubble mineralization typically involves a concentrated mineral deposit, while sedimentary exhalation can result in a dispersed blanket or thin crust of sedimentary ore.
Bubble mineralization is an important process in ore deposits, as it can significantly alter the composition, mineralogy and texture of the ore body. It is closely related to other ore formation processes, such as hydrothermal alteration, hydrothermal replacement, and sedimentary exhalation. Therefore, it is important to understand the nature and characteristics of bubble mineralization in order to identify economically viable ore reserves. Bubble mineralization can also be closely monitored and studied in order to identify ore-bearing areas and assess the size and concentration of mineralized elements within the ore deposit.
