外文翻譯--應用磁法勘探技術探查南非林波波河地區(qū)的地下情況

1、<p>　　中文2546字,1458單詞，7100英文字符</p><p><b>　　附錄</b></p><p><b>　　英文原文</b></p><p>　　Using the Magnetic Technique to Investigate the Subsurface in the Limpopo

2、 Region of South Africa</p><p>　　Mitchell L. Johnson</p><p>　　Jackson State University</p><p>　　AfricaArray 2009</p><p><b>　　Abstract</b></p><p&g

3、t;　　We employed the magnetic technique to take readings of the magnetic field in the Bushveld Complex. The Bushveld Complex is located in Limpopo, South Africa. The Bushveld Complex is known for its richness in natural r

4、esources. We are here to image a previously known dyke. This dyke has already been imaged by aeromagnetic data. Our ground magnetic survey will give one a better image of the dyke. Our survey consisted of 30 east-west li

5、nes that were 1000 meters long, oriented perpendicularly to a pr</p><p>　　Introduction</p><p>　　Magnetics is a branch of geophysics that studies how the properties or effects of magnetic fields

6、change in different places on the Earth. (McCarthy and Rubdige 2005). The Earth’s magnetic field can be thought of as a point on a surface, though it is generated by the movement of the fluid core, which consists of molt

7、en rock called magma. The magnetic field on the Earth will change because of differences in the geology of the surface. At a given location, the Earth’s magnetic field is described b</p><p>　　In this study,

8、we conducted geophysical investigations in the Bushveld Complex, located in the Limpopo Province in the northernmost part of South Africa (Fig. 1). </p><p>　　Fig. 1 Map of Bushveld Complex</p><p&g

9、t;　　The Bushveld Complex has an abundance of minerals that are mined. This area is known worldwide for these richest. (McCarthy and Rubidge 2005). By imaging the subsurface, we can assist mining companies to be more effi

10、cient. We can provide these companies with locations and images of what lies beneath the subsurface, preventing wasted time and money on trial and error exploration. </p><p>　　While in the Bushveld Complex w

11、e conducted a magnetic survey. This survey was used to map and locate a previously known dyke. Our results not only confirm the location of this large dyke, but also identify several smaller dykes in the vicinity. This i

12、s very pertinent for the mining industry. </p><p>　　Geologic background </p><p>　　The Bushveld Complex was formed around 2 billion years ago. There are 3 parts of the Bushveld Complex: an easter

13、n, western, and northern branch. All of these are very alike and were formed at about the same time. Magma from the Earth’s mantle that came to the surface made the Bushveld Igneous Complex. This continued to happen over

14、 a period of time. As the molten rock cooled over time, crystallization of different minerals at different temperatures lead to the formation layered structures were fo</p><p>　　One important layer is the Up

15、per Group 2 (UG2) reef The UG2 contains has chromite, platinum, and the Merensky Reef. The Merensky Reef has with a width of 30 to 90 cm and the UG2 contains have almost 90% of the worlds known PGE reserves. </p>

16、<p><b>　　Methods </b></p><p>　　Several geophysical methods were employed to investigate the subsurface structure of the Bushveld Complex however, for this study, I will focus on the magnetic

17、 method. The magnetic method depends on Coulomb’s Law, which describes the force generated by a magnetic field. </p><p>　　In this equation, F is the force, m1 and m2 are the strengths of two magnetic poles,

18、m is the magnetic permeability, and r is the distance between the two poles. (Burger et al., 2006) </p><p>　　To collect the magnetic data, an instrument called a magnetometer is used. This instrument measure

19、s the strength of the magnetic field at a particular location. The magnetometer does not measure position, but handheld GPS units can be used to determine the measurement location. </p><p>　　The magnetometer

20、 will not give a true reading if a reading is taken in the vicinity of metallic objects; therefore, readings should not be taken near railway lines, cars, houses and electric lines. These places and objects will change t

21、he magnetic field in the area. Also, the magnetometer operator should not carry metallic objects because these objects will have an influence on the magnetic field. </p><p>　　At our fieldsite, data was colle

22、cted along a grid of GPS coordinates, consisting of 30 lines that were 1000 meters long, striking roughly perpendicular to the dykes imaged by Anglo Platinum aeromagnetic data (Fig. 2). </p><p>　　Fig. 2 GPS

23、tracks overlaid on aeromagnetic data showing a known dyke</p><p>　　We were only able to survey 800 meters due to a power line and thorns in the vegetation. There were also 3 north-south lines that were condu

24、cted after the original survey had been completed. The survey line spacing was 25 meters between each line. We took a reading every 5 meters for the entire 800 meters of the survey line. A base station magnetometer was a

25、lso operated to measure diurnal variations, which was then used to correct our raw magnetic data. Diurnal variation is the repetitive variat</p><p><b>　　Results </b></p><p>　　Our mag

26、netic survey found one major magnetic dyke. This dyke is located around 15 meters below the surface. I was able to interpolate this by using 2D forward modeling. I tried to match the data collected in the field by placin

27、g dykes in the forward model (Fig 3). </p><p>　　Figure 3 2D Forward Model Profile</p><p>　　There is an overburden of 15 meters that has been previously found by Anglo Platinum. In addition to th

28、e main dyke, we also found 3 other anomalies that may be smaller dykes. </p><p>　　This is shown in a 3-D view of the survey data that has been interpolated. Next, we made a 2-D profile of the anomalies. We r

29、ealized that there is a secondary dyke that lies very close to our major dyke (Fig 4). </p><p>　　Figure 4. 3D view of data</p><p>　　Discussion </p><p>　　The major dyke imaged has a

30、northeast-southwest strike and has very high magnetic values, peaking at 4677 nT. (Fig. 3). The 3 other dykes that were imaged were smaller but were also deeper in the subsurface. One thing to take note of is that everyd

31、ay someone different took magnetic readings. This means that there may be readings that were taken that are not as accurate as others. </p><p>　　Another thing to take note of is that our magnetic data was co

32、llected on the ground, which is different than the aeromagnetic data collected by Anglo Platinum. The aeromagnetic survey is mainly used to map large areas. This is done by the use of an airplane flying over the survey a

33、rea. Ground magnetic surveys map smaller areas but in greater detail. Both have uses in the mining exploration. Some mineral deposits are associated with an increase in abundance of magnetic minerals. Ground magnetic s&l

34、t;/p><p>　　With the images we have produced of the Bushveld Complex, miners will know how and where to mine. A dyke is an intrusion of rocks into the natural geological structure and will be a weak point in the

35、 subsurface. If miners were to put a mine close to a dyke, the mine may become weak and collapse. This is very important because people’s lives will be at stake. </p><p>　　Conclusion </p><p>　　T

36、he magnetic method was employed to image the subsurface within the Bushveld Complex in Limpopo, South Africa. Using a magnetometer, we surveyed an area that consisted of 30 lines that were 800 meters long in search of ch

37、anges in the magnetic field. These changes in the magnetic field are important because certain minerals have a specific magnetic value and features, such as dykes, can be identified. Knowing the location of dykes in a fu

38、ture mining area will keep miners safe. We imaged one major</p><p>　　Acknowledgements </p><p>　　I would like to thank The Pennsylvania State University for being a part of the Summer Research Op

39、portunities Program. Dr. Andy Nyblabe for letting me participate in the AfricaArray program and field school. I would like to give thanks to My Mentors Dr. Samantha Hansen and Dr. Rick Brazier for their guidance and time

40、 that has been given to me this summer. Also, The University of Witwatersrand for hosting us. </p><p>　　References </p><p>　　Burger, R.H., Jones, C.H., Sheehan, A.F. Introduction to Applied Geop

41、hysics. Norton & Company, 2006. </p><p>　　McCarthy, T. and Rubidge, B. The Story of Earth & Life. South Africa: Struik, 2005. </p><p>　　U.S. Geological Survey. 2008. 13 July </p>

42、<p><b>　　文獻翻譯</b></p><p>　　應用磁法勘探技術探查南非林波波河地區(qū)的地下情況</p><p><b>　　摘要</b></p><p>　　我們采用磁技術在布什維爾德雜巖帶的磁場讀數(shù)。布什維爾德雜巖位于南非林波波河。布什維爾德雜巖以它豐富的天然資源而出名。我們在這里假設有一個先前已知的

43、堤壩。這個堤壩已經用航磁數(shù)據(jù)成像。我們的地面磁測將給一一個更好的圖像的堤壩。我們的調查是由30條東西線，長1000米，垂直于先前已知的堤壩，以及3條南北線跑這一地質特征。結果表明先前成像的堤防3小脈。這些數(shù)據(jù)可用于在測區(qū)未來礦業(yè)勘查。清楚地知道地下是什么能夠使礦工們以一個安全的和善于隨機應變方法在礦井里開采。</p><p><b>　　測區(qū)簡介</b></p><p&g

44、t;　　磁學是地球物理學的一個分支學科，主要研究磁場的變化屬性或磁域在不同的地方變化對地球的影響。（麥卡錫和rubdige 2005）。地球的磁場可以被認為是某一表面上的一點，但它是通過流體運動產生的核心，由熔化的巖石組成的那部分被稱為巖漿。由于地球表面地質的差異，地球上的磁場會發(fā)生改變。在一個給定的位置，地球磁場是一個由向量描述和使用單位奈特士拉測量的物理量。</p><p>　　在這項研究中，我們對位于南非林

45、波波省的最北端的布什維爾德雜巖進行了地球物理調查（如下圖1）。</p><p>　　圖1. 布什維爾德雜巖的地圖</p><p>　　布什維爾德雜巖有豐富的礦物質而且正在被開采。這個地區(qū)聞名全球主要是因為有這些豐富的資源。（麥卡錫和魯比奇2005）。為了更好地了解底下的情況，通過地下采礦公司的成像，對我們能幫助更有效。我們可以提供這些公司地表下面存在物質的具體位置和圖像，避免在試驗和錯

46、誤的探索上浪費太多的時間和金錢。</p><p>　　我們在布什維爾德雜巖地區(qū)進行了一項磁測量研究調查。這項調查是使用地圖并定位一個先前已知的堤壩。我們的研究結果不僅證實了這個大堤壩的位置，而且也確定了附近的幾個小堤壩的存在。這對采礦業(yè)的研究調查是非常中肯的。</p><p><b>　　測區(qū)的地質背景</b></p><p>　　布什維爾德雜

47、巖大約形成于二十億年前。布什維爾德雜巖主要有三個部分：一個是東方的，一個是西方的，還有一個是北方的分支。所有這些都是非常相似的，而且大約形成在同一時間。從地球的地幔出來的巖漿來到了地表形成了布什維爾德雜巖中的火成巖。這個變化持續(xù)了一段較長的時期。作為熔融巖石的冷卻時間，在不同溫度下的不同的礦物結晶導致形成層狀結構而形成的物質被稱為珊瑚礁。</p><p>　　其中一個重要的層是上組2（UG2）礁，UG2包含有鉻，

48、鉑，和Merensky礁。Merensky礁的寬度在30至90厘米之間，UG2包含有幾乎90%的世界上已知的PGE儲備。</p><p><b>　　勘探方法</b></p><p>　　多種地球物理勘探方法被用來對布什維爾德雜巖的地下結構進行調查，然而在這項研究調查中，我將會把重點放在磁法勘探上。磁方法依賴于庫侖定律，它描述了一個磁場產生的力。</p>

49、<p>　　在這個方程中，F(xiàn)是力，m1和m2是兩個磁極的長處，m是磁導率，而r是兩極之間的距離。（漢堡等人，2006）通過收集到的磁數(shù)據(jù)顯示，它是用了磁力計這種儀器。該儀器測量在一個特定位置的磁場強度。磁力儀測量不能顯示位置，但手持GPS單元可以用來確定具體的測量位置。</p><p>　　如果讀數(shù)時周圍有其他金屬物質，地磁儀將不能顯示出真實的數(shù)據(jù)。因此，讀數(shù)時應該盡量避開鐵路線，汽車，房子和電線等。

50、這些地方的對象將會引起在該地區(qū)的磁場的變化。同時，磁力計的操作人員也不應攜帶金屬物體，因為這些對象會對磁場變化有影響。</p><p>　　在我們的勘查區(qū)域，數(shù)據(jù)收集在一個GPS坐標網格內，由30條一千米長的線租成，驚人的大致垂直于墻英美鉑金航磁數(shù)據(jù)成像（如下圖2）。</p><p>　　圖2. 一個已知堤壩的GPS軌道重疊航磁數(shù)據(jù)顯示</p><p>　　由于電

51、源線和植被中的荊棘的影響，我們只能夠測量800米。這里有3條南北向的線，是在最初的調查時已經完成了的。每兩條測線之間的距離為25米。在800米的測長中我們采取了每隔五米讀取一組數(shù)據(jù)?；敬艔娪嫓y量也被用來測量測區(qū)的每天晝夜的變化規(guī)律，并被用來糾正我們的原磁數(shù)據(jù)。晝夜的變化就是地球磁場隨時間的不斷重復性變化（USGS 2008）。在每天收集好現(xiàn)場數(shù)據(jù)后勘測人員要對采集到的數(shù)據(jù)進行審核。這包括GPS讀數(shù)的采集和磁強計測量時的拍攝位置相關的字

52、段值，并轉換成Mag2D，在Excel中制作電子表格。</p><p><b>　　測量結果</b></p><p>　　我們的調查發(fā)現(xiàn)了一個主要磁脈磁。這個堤壩是位于約15米以下的表面。我能插用二維正演。我試圖將其放在先前的模型中與現(xiàn)場采集到的數(shù)據(jù)聯(lián)系起來（如下圖3）。</p><p>　　圖3. 二維正演模型簡介</p>&

53、lt;p>　　這有一條先前被發(fā)現(xiàn)的長15米的英美鉑金覆蓋層。除了這條主脈，我們也發(fā)現(xiàn)了其他3個異常，可能是較小的堤壩。</p><p>　　這個已經在一個三維視圖內插的調查數(shù)據(jù)中顯示出。接下來，我們做了一個異常的二維剖面。我們認識到還有有一個二級堤防，位于非常接近我們的主要堤防（如下圖4）。</p><p>　　圖4. 三維視圖的數(shù)據(jù)</p><p><

54、;b>　　探討</b></p><p>　　主要脈成像有西南東北走向，具有很高的磁場值，峰值在4677nT。（圖3）。其他三條脈成像較小但也存在于更深的地下。有一點需要注意的是，每天都有不同的人來讀取記錄磁性的數(shù)據(jù)。這意味著可能會出現(xiàn)采取的的讀數(shù)是那些不夠正確的人讀取的數(shù)據(jù)。</p><p>　　另一點需要注意的是，我們的磁數(shù)據(jù)是在地面上收集的，這是不同于由英美鉑金的航磁

55、數(shù)據(jù)的收集的。航磁調查主要用于大面積的映射。這是由一架飛機飛行在調查區(qū)域進行的。而地面磁測圖面積較小但是是更詳細的調查。兩種方法都已經用在礦業(yè)勘探中。一些礦物的沉積與磁性礦物豐富程度的增加相關。地面磁法測量將使我們能夠確定一個具體的磁讀，而在航磁調查只能給出該地區(qū)的概述。</p><p>　　根據(jù)我們給出的布什維爾德雜巖產生的圖像，礦工將會知道如何去開采和去哪里開采。堤防是巖石侵入的自然地質結構并成為在地下的薄弱

56、點。如果礦工把礦井建立在靠近堤處，礦井可能會比較軟弱和容易崩潰。這一點是非常重要的，因為人的生命將可能隨時處在危險之中。</p><p><b>　　結論</b></p><p>　　磁法勘探已經被用來反應林波波布什維爾德雜巖，南非等地區(qū)的地下區(qū)的圖像。利用磁強計，我們調查的一個地區(qū)，這是一個由30條長800米組成的測區(qū)內的磁場變化的調查。在磁場中的這些變化是很重要的

57、，因為每種確定的礦物都有一個具體的磁性礦物的價值和功能，比如堤壩，可以被識別。只有了解了一個堤壩的具體位置才能在未來的礦區(qū)開采中確保礦工的安全。我們拍攝并觀察了一個以前掌握的堤壩，我們也發(fā)現(xiàn)3個較小的堤壩。清楚的了解了地下是什么，英美鉑金將利用這些數(shù)據(jù)將進行進一步的安全和有效的處理自然資源勘探。</p><p><b>　　致謝</b></p><p>　　我要感謝濱

58、州州立大學成為夏季研究機會計劃的一部分。安迪博士讓我參加AfricaArray程序和田間學校。我要感謝我的導師薩曼莎博士漢森博士和瑞克他們給我的指導和時間，給了我這個夏天。同時，我還要感謝主辦方美國金山大學。</p><p><b>　　參考文獻</b></p><p>　　漢堡，相對濕度，瓊斯，C.H.，希恩，應用地球物理導論。諾頓公司，2006</p>