Mountaineer Partners Management, LLC — 13F Holdings & Portfolio
CIK 1730532 · latest 13F-HR filed 2026-08-13
Mountaineer Partners Management, LLC manages $132.0M in 13F-reported U.S. long-equity assets across 21 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are CENX (15.79%), SXT (10.54%), CSTM (10.01%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 1 new position and exited 6; 2 existing positions rose in reported value and 8 fell.
AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.
Long-equity book
Distinct positions
Filed 2026-08-13
vs 2026-03-31
Portfolio charts
Latest quarter's book, what changed, and how the portfolio has evolved across filings.
Portfolio map
Q2 26Box size = position value; colour = change in share count vs the prior quarter (green added, red trimmed, blue new). Rows split across managers or share classes are combined. Click a box for the stock.
Sector mix
% of 13F valueSectors from each company's SIC code; funds and ETFs grouped separately.
Biggest buys and sells
Q1 26 → Q2 26Estimated from the change in shares held × the quarter-end price, so price moves alone don't count as buying. New and exited positions are included.
13F assets and positions
4 quartersTotal reported 13F value (bars) and number of positions (line) each quarter. Value changes include market moves.
Top positions over time
reported valueThe eight largest current positions, valued at each quarter end.
Concentration
top 10 = 100%Cumulative share of the portfolio held in the largest N positions.
As of the firm’s regulatory filing dated Mar 31, 2026.
28TH FLOOR
NEW YORK, NY 10022
| Name | Title / Status | Ownership | Type |
|---|---|---|---|
| LEE, MARK, M Control | MANAGING MEMBER since May 2011 | 75% or more | Individual |
| WILLIAMS, GREGORY, STEPHEN Control | CHIEF COMPLIANCE OFFICER since Sep 2023 | Less than 5% | Individual |
Ownership & leadership changes · 5 filings with changes since Mar 27, 2012
From the firm’s regulatory filings, newest first. Dates are filing dates: a filing that no longer lists someone does not say when they left.
- No longer listedBORENSTEIN, DANIEL · CHIEF COMPLIANCE OFFICER / CHIEF FINANCIAL OFFICER · Less than 5% · control person · listed since Jan 2021
- Listed againWILLIAMS, GREGORY, STEPHEN · CHIEF COMPLIANCE OFFICER · Less than 5% · control person
- No longer listedHALLOWELL, JOHN, P. · MEMBER · 10–25% · control person · listed since May 2011
- No longer listedSIMON, MARC, DAVID · CHIEF FINANCIAL OFFICER/CHIEF COMPLIANCE OFFICER · 5–10% · control person · listed since Mar 2012
- No longer listedWILLIAMS, GREGORY, STEPHEN · MEMBER · 5–10% · listed since Mar 2017
- AddedBORENSTEIN, DANIEL · CHIEF COMPLIANCE OFFICER / CHIEF FINANCIAL OFFICER · Less than 5% · control person
- ChangedLEE, MARK, M · ownership 50–75% → 75% or more
- No longer listedBORTON, BENJAMIN, ALEXANDER · PRINCIPAL · 10–25% · control person · listed since Jan 2012
- ChangedHALLOWELL, JOHN, P. · ownership 5–10% → 10–25%
- AddedWILLIAMS, GREGORY, STEPHEN · MEMBER · 5–10%
- ListedBORTON, BENJAMIN, ALEXANDER · PRINCIPAL · 10–25% · control person
- ListedHALLOWELL, JOHN, P. · MEMBER · 5–10% · control person
- ListedLEE, MARK, M · MANAGING MEMBER · 50–75% · control person
- ListedSIMON, MARC, DAVID · CHIEF FINANCIAL OFFICER/CHIEF COMPLIANCE OFFICER · 5–10% · control person
Quarter-over-quarter changes
Changes in reported position value vs the prior 13F, so price moves count too, not just shares bought or sold.
Top Adds (vs prior quarter)
- STANDARDAERO INC$3.4M +32.0%
- SENSIENT TECHNOLOGIES CORP$2.7M +20.0%
Top Trims
- CENTURY ALUM CO-$11.1M -32.4%
- ARDAGH METAL PACKAGING S A-$4.9M -64.2%
- ALCOA CORP-$4.6M -30.0%
- ATI INC-$1.4M -10.8%
- CARPENTER TECHNOLOGY CORP-$1.3M -9.0%
Exited Positions
- HUDBAY MINERALS INC$14.8M
- FREEPORT MCMORAN INC$14.2M
- KIRBY CORP$11.8M
- D R HORTON INC$9.1M
- BUILDERS FIRSTSOURCE INC$8.1M
Mountaineer Partners Management, LLC Holdings (2026-06-30)
Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).
| # | Issuer | Symbol | CUSIP | Value | Weight | Shares | Type |
|---|---|---|---|---|---|---|---|
| 1 | CENTURY ALUM CO | CENX | 156431108 | $20.8M | 15.79% | 453,108 | SH |
| 2 | SENSIENT TECHNOLOGIES CORP | SXT | 81725T100 | $13.9M | 10.54% | 112,828 | SH |
| 3 | CONSTELLIUM SE | CSTM | F21107101 | $13.2M | 10.01% | 414,551 | SH |
| 4 | STANDARDAERO INC | SARO | 85423L103 | $11.4M | 8.67% | 382,784 | SH |
| 5 | CARPENTER TECHNOLOGY CORP | CRS | 144285103 | $10.5M | 7.96% | 17,034 | SH |
| 6 | ATI INC | ATI | 01741R102 | $9.6M | 7.24% | 48,502 | SH |
| 7 | MIDDLEBY CORP | MIDD | 596278101 | $9.3M | 7.03% | 53,982 | SH |
| 8 | ALCOA CORP | AA | 013872106 | $8.6M | 6.52% | 165,174 | SH |
| 9 | HARMONY GOLD MNG LTD | HMY | 413216300 | $7.4M | 5.60% | 486,256 | SH |
| 10 | CAMECO CORP | CCJ | 13321L108 | $3.1M | 2.38% | 30,786 | SH |
| 11 | ARDAGH METAL PACKAGING S A | AMBP | L02235106 | $2.7M | 2.06% | 574,207 | SH |
| 12 | STANDARDAERO INC | SARO | 85423L103 | $2.4M | 1.85% | 81,811 | SH |
| 13 | CARPENTER TECHNOLOGY CORP | CRS | 144285103 | $2.4M | 1.80% | 3,860 | SH |
| 14 | ATI INC | ATI | 01741R102 | $2.3M | 1.78% | 11,917 | SH |
| 15 | MIDDLEBY CORP | MIDD | 596278101 | $2.3M | 1.77% | 13,554 | SH |
| 16 | SENSIENT TECHNOLOGIES CORP | SXT | 81725T100 | $2.3M | 1.76% | 18,899 | SH |
| 17 | CENTURY ALUM CO | CENX | 156431108 | $2.3M | 1.75% | 50,201 | SH |
| 18 | ALCOA CORP | AA | 013872106 | $2.2M | 1.70% | 42,991 | SH |
| 19 | CONSTELLIUM SE | CSTM | F21107101 | $2.2M | 1.63% | 67,579 | SH |
| 20 | HARMONY GOLD MNG LTD | HMY | 413216300 | $1.9M | 1.46% | 126,693 | SH |
| 21 | CAMECO CORP | CCJ | 13321L108 | $928.7K | 0.70% | 9,117 | SH |
| Period | Filed | AUM | Holdings | Accession |
|---|---|---|---|---|
| 2026-06-30 | 2026-08-13 | $132.0M | 21 | 0000919574-26-005107 |
| 2026-06-30 | 2026-08-14 | $5.4M | 2 | 0000919574-26-005443 |
| 2026-03-31 | 2026-05-15 | $201.3M | 32 | 0000919574-26-003280 |
| 2025-12-31 | 2026-02-13 | $178.7M | 34 | 0000919574-26-000943 |
| 2025-09-30 | 2025-11-14 | $171.9M | 36 | 0000919574-25-006893 |
28TH FLOOR
NEW YORK, NY 10022