Crystallization, alteration, and ore-forming processes, of IOCG ores and related rocks

我未来五年的研究计划的总体目标是培养本科生和研究生更好地理解导致宿主岩石热液蚀变的地质过程，以及随后的矿化，经济级所谓的氧化铁磷灰石（IOA）和氧化铁铜金（IOCG）矿床。为了实现这一目标，我们将使用多种分析工具（经过详细的野外测绘和样品收集），包括：1)对未蚀变的乡村岩石、热液蚀变的寄主岩石、IOCG和IOA矿石中的锆石、独居石、磷灰石和钛矿进行原位U-Pb年代学分析；2)原位微量元素和示踪同位素，包括Sm-Nd、Lu-Hf和Pb-Pb，在相同的附属相中（在熔融包裹体中Pb-Pb的情况下），以及锆石中的原位O同位素；3)未蚀变围岩、热液蚀变宿主岩、IOCG和IOA矿石的全岩主微量元素和Sm-Nd、Lu-Hf、Pb-Pb和Rb-Sr示踪同位素。该研究计划的拟议实地区域包括两个地点：1)瑞典北部的Norrbotten地区；智利北部的阿塔卡马沙漠地区。在北部地区（如Kiirunavaara和Per Geijer矿石）和Svappavaara（如Gruvberget、Mertainen和Leveäniemi矿石），我的研究计划的下一阶段将建立在我目前的博士生所获得的结果之上，他主要研究Kiirunavaara和Per Geijer矿石。该研究结果通过锆石和钛矿的原位U-Pb年代学证实了北博顿地区1880-1900 Ma左右的地质事件。更有趣的是，最近从几个矿石样品中获得的独居石U-Pb结果表明，1624±22 Ma的事件发生较晚。此外，Sm-Nd同位素全岩数据显示，未蚀变寄主岩（eNd ~ -6）、强蚀变寄主岩（~3.5 ~ -4）和矿石（eNd ~ -3）之间存在明显差异，可能表明后两者受到了枯竭地幔的影响。这种Nd同位素组成的差异可能是由矿石内独居石中U-Pb系统记录的同一事件引起的。需要在该地区进一步研究以证实这些发现，并通过调查瑞典北部地区（如Svappavaara）的其他此类矿床来了解铁成矿与这两个事件的关系。IOA IOCG与斑岩矿床之间的关系尚不清楚。例如，许多研究使用流体包裹体、稳定同位素和放射性同位素来了解加拿大、澳大利亚和南美洲的IOCG矿床。比较这些庞大的数据集，并以系统的方式收集新数据，就像我们小组所做的基鲁纳工作一样，可以帮助了解两种矿床类型之间的异同，并帮助了解它们的形成。为了解决这个问题，我还计划在智利北部的两个领域采用与瑞典类似的方法开始这项工作：1)第一个地区是El Laco，一个著名的新近（~2 Ma）火山，含有大约10亿吨铁，具有磁铁矿熔岩流和磁铁矿石等特征；2)第二个油田区是智利地区，那里有许多IOCG和IOA矿床（例如Tropezón， Filomena, Carola, La Farola, Romeral）。最后，我计划在我的实验地球化学实验室中生长和表征（使用粉末XRD， EPMA， Raman和LA-ICPMS）合成锆石，独居石，钛矿和磷灰石，以便更好地了解它们的晶体化学和电荷平衡机制，以便在IOCG和IOA矿石中经常发现高浓度的微量元素。

The overarching objective of my research program for the next five years is to train undergraduate and graduate students to better understand the geologic processes that lead to the hydrothermal alteration of host rocks, and subsequent mineralization, of economic grade so-called iron oxide apatite (IOA) and iron oxide copper gold (IOCG) deposits. To accomplish this, we will use a combination of analytical tools (after detailed field mapping and sample collection) including: 1) In situ U-Pb geochronology of zircon, monazite, apatite, and titanite from unaltered country rocks, hydrothermally altered host rocks, and IOCG and IOA ores; 2) in situ trace elements and tracer isotopes including Sm-Nd, Lu-Hf, and Pb-Pb, in the same accessory phases (and in the case of Pb-Pb in melt inclusions) and where appropriate, in situ O isotopes in zircon; and 3) whole rock major and trace elements and Sm-Nd, Lu-Hf, Pb-Pb and Rb-Sr tracer isotopes, from unaltered country rock, hydrothermally altered host rock, and IOCG and IOA ores. The proposed field areas for this research program includes two locations: 1) The Norrbotten region of northern Sweden and; 2) the Atacama Desert region of northern Chile. In the Norrbotten region (e.g., the Kiirunavaara and Per Geijer ores), and Svappavaara (e.g., the Gruvberget, Mertainen and Leveäniemi ores), the next phase of my research program will build on the results obtained by my current Ph.D. student who has been working primarily on the Kiirunavaara and Per Geijer ores. The results of that research has confirmed a geologic event around 1880-1900 Ma in the Norrbotten region by using in situ U-Pb geochronology of zircon and titanite. More interesting, recent U-Pb in monazite results from several ore samples suggests a later event at 1624 ±22 Ma. Furthermore, Sm-Nd isotopic whole rock data shows distinct differences between the unaltered host rocks (eNd ~ -6), strongly altered host rocks (~3.5 to -4), and the ore (eNd ~ -3), possibly indicating a depleted mantle influence for the latter two. This difference in the Nd isotopic composition may be caused by the same event that is recorded by the U-Pb system in monazite within the ore. Further study in this region is needed to confirm these findings and understand how the iron mineralization is related to the two events by investigating other such deposits in the Norrbotten region of Sweden such as Svappavaara. The relationship between IOA IOCG and porphyry deposits is far from clear. A number of studies have used fluid inclusions, and stable and radiogenic isotopes, to understand IOCG deposits in Canada, Australia and South America, for instance. Comparing this vast data set, and collecting new data in a systematic way like the Kiruna work that has been done by our group, could help to understand similarities and differences between the two deposit types and help understand their formation. To address this, I also plan to begin this work following a similar approach as in Sweden, in northern Chile in two field areas: 1) The first area is El Laco, a well-known recent (~2 Ma) volcano that contains roughly 1 billion tons of Fe and has features such as magnetite lava flows and magnetite lapilli; 2) The second field area is the region of Chile where there are numerous IOCG and IOA deposits (e.g., Tropezón, Filomena, Carola, La Farola, Romeral). Lastly, I plan to grow and characterize (using powder XRD, EPMA, Raman and LA-ICPMS) synthetic zircon, monazite, titanite, and apatite in my experimental geochemistry laboratory in order to better understand their crystal chemistry and charge balancing mechanisms that allow for the incorporation trace elements in the high concentrations they are often found in IOCG and IOA ores.