The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) deposits containing magnetite and rare earth element (REE)-bearing apatite. We use new aeromagnetic, aeroradiometric, ground gravity, and sample petrophysical and geochemical data to image and understand these deposits and their geologic framework. Aeromagnetic total field data reflect highly magnetic leucogranite host rock and major structures that likely served as fluid conduits for the hydrothermal system. Band-pass filtering of the aeromagnetic data reveals locations of individual deposits that were verified in the field or from historical records. A 3D inversion for magnetic susceptibility images these deposits at depth, allowing the inference of plunge directions and relative size. Radiometric data highlight variations in the surface geology and several large tailings piles that contain REE-bearing apatite. Within the host rock, eTh (equivalent Th), K, and the eTh/K ratio are variable with high eTh/K near several of the IOA deposits. Areas with elevated K or low eTh/K representing potassic alteration appear to be rare; instead, elevated eTh/K ratios likely reflect widespread sodic alteration that overprinted potassic alteration. Bouguer gravity anomalies show limited correspondence to the surface geology, radiometric data, or magnetic data, but they do exhibit approximately 10 km wide highs in areas where deposits are observed. Some 2D forward models of the gravity and magnetic data show that deeper dense material beneath the leucogranite is quantitatively feasible. If these dense rocks represent intrusions that were emplaced or still cooling at the time of mineralization, they may have served as a heat source that helped to drive the hydrothermal system. Combining data sets, we find that deposits occur toward the distal ends of major structures within the host leucogranite and mostly above gravity highs. The geophysical modeling thus suggests that IOA deposits formed in structural, thermal, and chemical traps near the distal ends of the hydrothermal system.

中文翻译：

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纽约东阿迪朗达克高地含稀土元素的氧化铁-磷灰石矿床的综合地球物理成像

纽约州北部的阿迪朗达克高原（Adirondack Highlands）拥有数十个氧化铁-磷灰石（IOA）矿床，其中含有磁铁矿和稀土元素（REE）磷灰石。我们使用新的航空磁，航空辐射测量，地面重力以及样品岩石物理和地球化学数据来成像和了解这些矿床及其地质框架。航磁总场数据反映了高磁性白云石基质岩石和主要结构，它们很可能充当了热液系统的流体管道。航空数据的带通滤波显示了在现场或从历史记录中验证的单个矿床的位置。磁化率的3D反演对这些沉积物进行了深度成像，从而可以推断出倾角方向和相对大小。辐射数据突出了地表地质的变化，并发现了一些大型含稀土元素的尾矿堆。在基质岩中，随着几个IOA矿床附近eTh / K的升高，eTh（等效Th），K和eTh / K的比值会发生变化。K升高或eTh / K较低代表钾质改变的区域似乎很少；取而代之的是，eTh / K比率升高可能反映了广泛的钠离子变化，而后者覆盖了钾离子的变化。布格重力异常与地表地质，辐射数据或磁数据的对应关系有限，但在观察到沉积物的区域中确实表现出约10 km宽的高。一些重力和磁数据的二维正演模型表明，白云石下方较深的致密物质在定量上是可行的。如果这些致密的岩石代表在矿化时已被侵入或仍在冷却的侵入岩，则它们可能是帮助推动水热系统的热源。结合数据集，我们发现沉积物朝着主体无色花岗岩内部主要结构的远端发生，并且大多在重力高点以上。因此，地球物理模型表明，IOA沉积物形成于热液系统远端附近的结构，热和化学阱中。