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首页> 外文期刊>Michigan Academician >Distribution of Magnetic Sands on Lake Michigan Beaches near Milwaukee, Wisconsin
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Distribution of Magnetic Sands on Lake Michigan Beaches near Milwaukee, Wisconsin

机译：威斯康星州密尔沃基附近的密歇根湖海滩上的磁性沙分布

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We initiated a study on a beach 10 km north of Milwaukee at Doctors Park to determine possible sources of the magnetite-enriched sand that has varied from 1-20% over the past 5 years. Samples were collected once a month from September to December 2001 at locations near the mouth of an ephemeral stream and on the north side of three groins at the beach. Magnetic susceptibility measurements of the sand samples were used as an indication of the amount of ferromagnetic minerals present. Magnetic susceptibility values for the four locations at Doctors Park―and for beaches as much as 50 km away―were similar, containing an equivalent of 1-2% by weight of magnetite. We suspect that increased erosion of the till bluffs during high lake levels five years ago (1998-99) provided new sediment sources, and the longshore transport concentrated the heavy minerals near the two beaches that are located at promontories on the shoreline. These sands contain as much as 20% magnetite and appear to be unrelated to the stream flow. Magnetic separation using a Franz Magnetic Separator provides evidence that the 1998 samples also have higher concentrations of paramagnetic minerals such as amphiboles and pyroxenes compared to the sands found on the present day beaches. This suggests that the source of the concentrations of heavy mineral sands is away from the immediate area and not from the drainage region of the small streams.
机译：我们在博士公园以北10公里处的密尔沃基以北的海滩上进行了一项研究，以确定富含磁铁矿砂的可能来源，在过去5年中，这种来源的比例在1-20％之间变化。从2001年9月到2001年12月，每月在一次短暂河口附近和海滩上三个腹股沟的北侧收集样品。砂样品的磁化率测量值用来指示存在的铁磁性矿物的数量。 Doctors Park的四个位置（以及距50公里之遥的海滩）的磁化率值相似，包含相当于磁铁矿重量1-2％的磁化率。我们怀疑，五年前（1998-99年）高湖水位期间，耕作till的侵蚀加剧，提供了新的沉积物来源，而长岸运输将重金属矿物集中在位于海岸线海角的两个海滩附近。这些沙子含有多达20％的磁铁矿，似乎与水流无关。使用Franz磁选机进行磁选提供的证据表明，与当今海滩上的沙子相比，1998年的样品还含有较高浓度的顺磁矿物，如闪石和辉石。这表明重矿物砂浓度的来源远离直接区域而不是小溪流的排水区域。

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