图  1  研究区区域地质背景图

a—中上扬子区早寒武世梅树村期沉积古地理图（牟传龙等，2012）；b—四川马边县黄家坪磷矿北东部矿区地质简图

Figure  1.  Regional geological map of the study area

(a) Sedimentary facies and palaeogeography in the middle-upper Yangtze area during the Early Cambrian Meishucunian (Mou et al., 2012); (b) Geological sketch of northeast Huangjiaping phosphate deposit, Mabian County, Sichuan Province

图  2  马边黄家坪磷矿下寒武统麦地坪组沉积相综合柱状图

Figure  2.  Synthetical histogram of sedimentary facies of the lower Cambrian Maidiping formation in the Huangjiaping phosphate deposit, Mabian County

图  3  马边黄家坪磷矿下寒武统麦地坪组典型沉积特征和显微镜下特征

Є₁ m ¹—麦地坪组一段；Є₁ m ²—麦地坪组二段；Z₂ dn ⁴—灯影组四段a—麦地坪组宏观照；b—磷矿层宏观照（图3a中方框放大），箭头处见硅质白云岩透镜体；c—水云母黏土岩；d—瘤状灰岩；e—筇竹寺组炭质泥岩与麦地坪组白云岩呈平行不整合接触；f—含磷质砾屑白云岩，砾屑杂乱分布；g—砂屑磷块岩，砂屑多呈圆形、椭圆形，填隙物多为不规则状泥晶胶磷矿及白云石（+）；h—砂砾屑磷块岩，发育多期冲刷面、正粒序层理组成的沉积序列；i—砂砾屑磷块岩，发育多期冲刷面、正粒序层理组成的沉积序列

Figure  3.  Typical sedimentary features and microscopic characteristics of the lower Cambrian Maidiping formation in the Huangjiaping phosphate deposit, Mabian County

(a) Macrophotograph of the Maidiping formation; (b) Macrophotograph of the phosphorite layer (enlarged by the box in Fig 3a), and siliceous dolomitite lenticle is seen at the arrow; (c) Hydromica clay rock; (d) Nodular limestone; (e) The carbonaceous mudstone of the Qiongzhusi formation is in disconformity with the dolomites of the Maidiping formation; (f) Phosphorus-bearing dolomite with phosphorus gravels disorderly distributed; (g) Arenite phosphorite, mostly with round, oval arenite and irregular micritecollophanite and dolomite as interstitial materials (+); (h) Sand-gravel phosphorite, developed with a sedimentary sequence consisting of multi-stage scouring surface and normal graded bedding; (i) Sand-gravel phosphorite, developed with a sedimentary sequence consisting of multi-stage erosion surface and normal graded bedding Є₁ m ¹–the first member of the Maidiping formation; Є₁ m ²–the second member of the Maidiping formation; Z₂ dn ⁴–the fourth member of the Dengying formation

图  4  马边黄家坪磷矿下寒武统麦地坪组一段磷矿层沉积特征和显微结构特征

a—条纹条带状磷块岩，夹硅质透镜体，磷块岩呈透镜状断续分布；b—致密块状砂砾屑磷块岩，夹少量白云质条纹；c—含磷白云岩，发育脉状层理；d—砂砾屑磷块岩，发育微波状层理；e—砂屑磷块岩，发育磷质鲕粒结构，磷质颗粒周缘发育磷质环边包壳，长轴方向具有一定定向性（+）；f—硅质白云岩，发育硅质条带、水平纹层；g—含磷硅质白云岩，夹硅质透镜体； h—含磷细晶白云岩（+）；i—磷质细晶白云岩，胶磷矿多为椭球型或不规则型砂屑（+）；j—含磷硅质白云岩，夹硅质透镜体，具水平层理；k—含磷水云母黏土岩，具水平层理

Figure  4.  Sedimentary features and microstructures of phosphate rocks in the first member of the lower Cambrian Maidiping formation in the Huangjiaping phosphate deposit, Mabian County

(a) Banded phosphorite, intercalated with siliceous lenticle, is intermittently distributed in a lenticular pattern; (b) Dense massive sand-gravel phosphorite interspersed with dolomite stripes; (c) Phosphorus-bearing dolomite with veined beddings; (d) Sand-gravel phosphorite with micro wavy beddings; (e) Arenite phosphorite, with phosphorus oolitic structure. Phosphorus crust is developed around the grain, with certain orientation along the long axis (+); (f) Siliceous dolomitite with siliceous bands and horizontal laminations; (g) Phosphorus-bearing siliceous dolomitite intercalated with siliceous lenticular; (h) Phosphorus-bearing fine-crystalline dolomite (+); (i) Phosphorous fine-crystalline dolomite, and collophanites are mostly ellipsoid or irregular arenes (+); (j) Phosphorus-bearing siliceous dolomitite intercalated with siliceous lenticular and horizontal beddings; (k) Phosphorus-bearing hydromica clay rock with horizontal beddings

图  5  马边黄家坪磷矿下寒武统麦地坪组二段沉积构造和显微镜下特征

a—黏土岩，具泥状结构（+）；b—瘤状灰岩，瘤体内含较多生物碎屑及磷质砾屑，瘤体边缘有明显的溶蚀痕迹，基质为泥质；c—瘤状灰岩（图5b中方框放大）；d—含磷屑细晶白云岩，见部分胶磷矿砾屑包裹细小白云石、石英颗粒（+）；e—含磷屑砾屑白云岩，可见棒状砾屑直立分布；f—含磷质砾屑细晶白云岩，砾屑具定向性；g—细−粉晶白云岩，发育鸟眼构造；h—含磷屑白云岩，发育齿状石膏溶孔

Figure  5.  Sedimentary characteristics and microscopic characteristics of of the second member of the lower Cambrian Maidiping formation in the Huangjiaping phosphate deposit of Mabian County

(a) Clay rock with muddy texture (+); (b) Nodular limestone with bioclasts and phosphorous gravels in the tumour-body and obvious corrosion traces at the edge of the tumour-body, and the matrix is argillaceous; (c) Nodular limestone (enlarged by the box in Fig 5b); (d) Phosphorus-bearing fine-crystalline dolomites with some collophanite gravels wrapped with fine dolomite and quartz particles (+); (e) Phosphorus-bearing dolorudite with rodlike gravel-sized grain vertical distributed; (f) Phosphorus-bearing fine-crystalline dolostones with orientation; (g) Fine-powder crystalline dolostones with bird’s eye structure; (h) Phosphorus-bearing dolomite with dentoid gypsum dissolution pores

图  6  马边黄家坪磷矿下寒武统麦地坪组磷成矿模式图

a—麦地坪组沉积模式图；b—磷块岩富集模式图（①、②、③分别对应图6a中位置；①为磷初始富集阶段，受间歇性水流冲刷，形成少量纹层状或条带状含磷沉积物，②、③为后期受强水流冲刷、簸选作用，分别形成高品位条纹条带状磷块岩或致密块状磷块岩）

Figure  6.  Phosphorus mineralization model of the lower Cambrian Maidiping formation in the Huangjiaping phosphate deposit, Mabian County

(a) Sedimentary model of the Maidiping formation; (b) Enrichment model of phosphorite, and ①, ② and ③ correspond to the positions in Fig. 6a respectively. ① represents the initial phosphorite enrichment stage, in which a small amount of laminar or banded phosphorus sediments were formed by the intermittent water scouring; ② and ③ are the later stages, where high-grade striped or dense massive phosphorites were formed under the action of scouring and winnowing, respectively.