川东北宣汉地区海相“新型杂卤石钾盐矿”的发现、突破与前景

Discovery,breakthrough and prospect of“new type polyhalite potash deposit”in the Puguang area,northeastern Sichuan basin

全球探明钾盐资源主体为古代海相可溶性固体钾盐矿床(氯化钾、光卤石),仅少量来自现代盐湖卤水钾矿。与国外不同的是,目前我国探明钾盐资源主体为现代陆相盐湖钾矿,古代海相可溶性固体钾盐找矿40余年,未获突破。四川盆地是我国主要大型海相成钾盆地之一,前人在中—下三叠统发现大量与硬石膏和白云石共伴生或互层的杂卤石,但绝大部分埋深超过2000 m,目前尚难以开发利用。2017年以来,笔者通过对四川盆地东北部宣汉盐盆普光地区卤水探井(恒成2、3井)岩芯复查,发现杂卤石主要与石盐共伴生,大量破碎的杂卤石碎屑颗粒分布于石盐基质中,KCl含量达边界工业品位以上,不同于钾石盐和光卤石,亦不同于前人发现的与硬石膏和白云石共伴生或互层的杂卤石(石膏型杂卤石),将之命名为“新型杂卤石钾盐矿”。小试和中试结果表明,该“新型杂卤石钾盐矿”可以采用对接井注水溶采,是能够得到规模化开发利用的“活矿”,是一种全新的硫酸盐+氯化物复合型海相可溶性固体钾盐矿床新类型。通过成钾条件、成矿规律综合研究,笔者提出了新型杂卤石钾盐矿“双控复合成矿”理论新认识、建立了“三高、两低、一大”综合测井识别新模型,创新理论技术指导设计部署“钾锂兼探”基准井——川宣地1井,探获厚29.46 m、氯化钾(KCl)平均含量12.03%(最高20.5%)的“新型杂卤石钾盐矿”厚层高品位工业矿层。与此同时,采用岩芯样品实测数据和测井解释数据拟合的方法,建立矿石K含量和密度参数的测井定量预测模型,结合“气钾兼探”,利用33口钻井数据,依据古代固体盐类勘查规范(2020),运用“几何法”,初步估算“新型杂卤石钾盐矿”氯化钾(KCl)资源规模:推断资源量2.45亿t(超大型)、潜在资源4.65亿t,合计7.1亿t,奠定了川东北达州市宣汉地区形成中国首个亿吨级海相钾盐基地的资源基础,取得了我国海相可溶性固体钾盐找矿的重大突破。

Globally,the majority of proven potassium salt resources are ancient marine soluble solid deposits(sylvine,carnallite).In contrast,Chinas proven potassium salt resources mainly originate from modern salt lake brines.Despite decades of exploration,breakthroughs in marine soluble solid potassium salt prospecting in ancient salt basins have remained elusive.The Sichuan basin,a major marine potassiumforming basin in China,harbors significant polyhalite deposits associated with or interbedded with anhydrite and dolomite in the Middle and Lower Triassic series.However,these deposits are generally buried at depths exceeding 2000 m,posing significant challenges for development and utilization.Since 2017,core reviews from brine exploration wells(HC2 and HC3)in the Xuanhan salt basin of the Puguang area in the northeastern Sichuan basin have revealed a type of polyhalite-type potassium-bearing ore.This“new type polyhalite potassium ore”is characterized by the abundant fragmented polyhalite dispersed in the salt matrix and exhibiting a converted KCl content exceeding industrial grade thresholds.This type of polyhalite,known as“new type polyhalite potassium ore,”differs from sylvite,carnallite,and the polyhalite associated or interbedded with anhydrite and dolomite(anhydrite-type polyhalite)discovered by predecessors.Small-and medium-scale tests show that this“new type polyhalite potassium ore”can be dissolved by water injection through butt wells;therefore,it is a“live ore”that can be developed and utilized on a large scale.It is also a new type of sulfate-chloride composite marine soluble solid potassium salt deposit.A thick industrial layer of“new type polyhalite potassium ore”with a thickness of 29.46 m and an average KCl content of 12.03%(reaching a maximum of 20.5%)was discovered in the“potassium-lithium exploration”reference well CXD 1.This discovery,based on the“double controlled compound”metallogenic theory,marks a substantial breakthrough in marine soluble solid potassium salt prospecting in China.Furthermore,a quantitative prediction model for K content and density parameters of the ore was established by fitting measured core sample data and logging interpretation data.Utilizing the“gas-potassium exploration”method and data from 33 wells,the KCl resource of the“new type polyhalite potassium ore”was preliminary estimated using the“geometric method,”referring to the ancient solid salt exploration code(2020).The estimated inferred resource is 245 million tons(super-large scale),with potential resources reaching 465 million tons,totaling 710 million tons.This discovery lays the foundation for establishing Chinas first 100-million-ton-class marine potassium salt base in Xuanhan County,Dazhou City,northeastern Sichuan Province,and represents a major breakthrough in Chinas search for marine soluble solid potassium ore.