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Mountaineer Partners Management, LLC

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13F filer, CIK 1730532, New York, NY

Mountaineer Partners Management, LLC reported $201,324,463 across 16 holdings for the quarter ended 2026-03-31, in a 13F-HR filed 2026-05-15. Its ten largest share positions make up 78.62% of the portfolio.

Filed (acceptance time not in the bulk data set), ingested 13F-HR 0000919574-26-003280

Period
2026-03-31
Reported value
$201M
Holdings
16
Top 10 weight
78.62%
New
1
Sold out
2

Largest buys vs the previous quarter

SecurityShares changeApprox. value
HMYnew+666,735$10.2M
SXTadded+39,494$3.41M
AMBPadded+408,602$1.65M
SAROadded+39,937$1.03M
BLDRadded+4,112$339K

Ranked by the share change valued at this quarter's implied price (value over shares in the 13F). A position sold out is valued at the previous quarter's price, its last report.

Largest sells vs the previous quarter

SecurityShares changeApprox. value
ATIreduced-37,125-$5.4M
NXEexited-538,042-$4.95M
SJTexited-732,351-$4.12M
HBMreduced-81,207-$1.7M
FCXreduced-25,354-$1.49M

Ranked by the share change valued at this quarter's implied price (value over shares in the 13F). A position sold out is valued at the previous quarter's price, its last report.

Holdings, Q1 2026

Share positions as resolved from 13F-HR 0000919574-26-003280, largest first. % of portfolio is the value over $201,324,463, the sum of the share positions whose value is usable for ratios (method).

SecurityHistorySharesValue% of portfolioChangeLatest eventTimeline
CENXCENTURY ALUM COQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 1,407,831 shares; 2024Q4: 647,845 shares; 2025Q1: 639,373 shares; 2025Q2: 705,150 shares; 2025Q3: 661,043 shares; 2025Q4: 608,475 shares; 2026Q1: 583,997 shares 583,997$34.3M17.02%-24,478Timeline
CSTMCONSTELLIUM SEQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 549,134 shares; 2024Q4: 887,239 shares; 2025Q1: 542,068 shares; 2025Q2: 845,682 shares; 2025Q3: 833,776 shares; 2025Q4: 681,464 shares; 2026Q1: 658,490 shares 658,490$16.2M8.04%-22,974Timeline
AAALCOA CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 279,831 shares; 2024Q4: 257,778 shares; 2025Q1: 265,965 shares; 2025Q2: 304,781 shares; 2025Q3: 296,642 shares; 2025Q4: 241,994 shares; 2026Q1: 233,687 shares 233,687$15.5M7.7%-8,307Timeline
HBMHUDBAY MINERALS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 1,123,352 shares; 2024Q4: 1,104,563 shares; 2025Q1: 1,161,055 shares; 2025Q2: 1,124,432 shares; 2025Q3: 955,419 shares; 2025Q4: 787,247 shares; 2026Q1: 706,040 shares 706,040$14.8M7.33%-81,207Timeline
FCXFREEPORT MCMORAN INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 239,045 shares; 2024Q4: 246,840 shares; 2025Q1: 250,558 shares; 2025Q2: 252,961 shares; 2025Q3: 294,049 shares; 2025Q4: 266,327 shares; 2026Q1: 240,973 shares 240,973$14.2M7.04%-25,354Timeline
CRSCARPENTER TECHNOLOGY CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 39,982 shares; 2025Q3: 40,849 shares; 2025Q4: 36,690 shares; 2026Q1: 35,929 shares 35,929$14.2M7.03%-761Timeline
SXTSENSIENT TECHNOLOGIES CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 117,090 shares; 2026Q1: 156,584 shares 156,584$13.5M6.72%+39,494Timeline
ATIATI INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 140,650 shares; 2024Q4: 182,670 shares; 2025Q1: 181,375 shares; 2025Q2: 122,970 shares; 2025Q3: 144,020 shares; 2025Q4: 128,909 shares; 2026Q1: 91,784 shares 91,784$13.4M6.63%-37,125Timeline
KEXKIRBY CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 65,431 shares; 2025Q3: 65,431 shares; 2025Q4: 87,444 shares; 2026Q1: 89,017 shares 89,017$11.8M5.88%+1,573Timeline
SAROSTANDARDAERO INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 290,730 shares; 2025Q3: 290,730 shares; 2025Q4: 367,498 shares; 2026Q1: 407,435 shares 407,435$10.5M5.23%+39,937Timeline
HMYHARMONY GOLD MNG LTDQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 666,735 shares 666,735$10.2M5.09%newTimeline
DHID R HORTON INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 50,921 shares; 2024Q4: 51,015 shares; 2025Q1: 53,655 shares; 2025Q2: not reported; 2025Q3: 27,876 shares; 2025Q4: 65,004 shares; 2026Q1: 66,541 shares 66,541$9.13M4.54%+1,537Timeline
BLDRBUILDERS FIRSTSOURCE INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 55,875 shares; 2024Q4: 55,875 shares; 2025Q1: 58,211 shares; 2025Q2: 62,464 shares; 2025Q3: 60,759 shares; 2025Q4: 94,091 shares; 2026Q1: 98,203 shares 98,203$8.09M4.02%+4,112Timeline
AMBPARDAGH METAL PACKAGING S AQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: 1,057,720 shares; 2025Q1: 1,057,720 shares; 2025Q2: 1,538,484 shares; 2025Q3: 1,538,484 shares; 2025Q4: 1,469,480 shares; 2026Q1: 1,878,082 shares 1,878,082$7.61M3.78%+408,602Timeline
CCJCAMECO CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 42,424 shares; 2026Q1: 42,424 shares 42,424$4.61M2.29%0Timeline
ULCCFRONTIER GROUP HLDGS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 953,375 shares; 2026Q1: 953,375 shares 953,375$3.37M1.67%0Timeline

Sold out in Q1 2026

Positions in the previous quarter's report that this quarter's report no longer lists.

SecurityShares beforeValue beforeType
NXENEXGEN ENERGY LTD538,042$4.95Mshares
SJTSAN JUAN BASIN RTY TR732,351$4.12Mshares

How Q1 2026 was built

Available 13F filings of this filer for the quarter and their roles: the base report is the latest original or restatement, NEW HOLDINGS amendments filed after it are added (method).

FilingRoleAmendmentFiledAcceptedIngested
13F-HR 0000919574-26-003280 base2026-05-15acceptance time not in the bulk data set